Updated on 2024/02/03

写真b

 
HIRAMATSU Takashi
 
*Items subject to periodic update by Rikkyo University (The rest are reprinted from information registered on researchmap.)
Affiliation*
College of Science Department of Physics
Title*
Assistant Professor
Degree
博士(理学) ( 東京大学 )
Research Interests
  • cosmological perturbations

  • modified theories of gravity

  • numerical cosmology

  • reheating process

  • topological defects

  • cosmic string

  • cosmic microwave background

  • gravitational waves

  • cosmology

  • Campus Career*
    • 4 2020 - Present 
      College of Science   Department of Physics   Assistant Professor
     

    Research Areas

    • Natural Science / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics  / cosmology

    Research History

    • 4 2020 - Present 
      Rikkyo University   Department of Physics, College of Science   Assistant Professor

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    • 4 2019 - 3 2020 
      The University of Tokyo   Institute for Cosmic Ray Research   ICRR fellow

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    • 9 2016 - 3 2019 
      Rikkyo University   Department of Physics, Collage of Science   Postdoctoral fellow

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    • 4 2016 - 8 2016 
      University of Kyoto   Yukawa Institute for Theoretical Physics   Research fellow

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    • 4 2011 - 3 2016 
      University of Kyoto   Yukawa Institute for Theoretical Physics   Program-specific Researcher

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    • 4 2010 - 3 2011 
      University of Kyoto   Yukawa Institute for Theoretical Physics   Research fellow

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    • 4 2008 - 3 2010 
      The University of Tokyo   Institute for Cosmic Ray Research   Research fellow

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    • 4 2007 - 3 2008 
      The University of Tokyo   Research Center for the Early Universe   Research fellow

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    ▼display all

    Education

    • 4 2004 - 3 2007 
      The University of Tokyo   Graduate school of Science   Department of Physics, Doctor's course

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    • 4 2002 - 3 2004 
      The University of Tokyo   Graduate school of Science   Department of Physics, Master's cource

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    • 4 2000 - 3 2002 
      The University of Tokyo   School of Science   Department of Physics

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    • 4 1998 - 3 2000 
      The University of Tokyo   Collage of Arts and Sciences   Natural Sciences I

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    Papers

    • Cosmological gravity probes: connecting recent theoretical developments to forthcoming observations Peer-reviewed

      Shun Arai, Katsuki Aoki, Yuji Chinone, Rampei Kimura, Tsutomu Kobayashi, Hironao Miyatake, Daisuke Yamauchi, Shuichiro Yokoyama, Kazuyuki Akitsu, Takashi Hiramatsu, Shin’ichi Hirano, Ryotaro Kase, Taishi Katsuragawa, Yosuke Kobayashi, Toshiya Namikawa, Takahiro Nishimichi, Teppei Okumura, Maresuke Shiraishi, Masato Shirasaki, Tomomi Sunayama, Kazufumi Takahashi, Atsushi Taruya, Junsei Tokuda

      Progress of Theoretical and Experimental Physics2023 ( 7 )   27 4 2023

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      Publishing type:Research paper (scientific journal)   Publisher:Oxford University Press (OUP)  

      Abstract

      Since the discovery of the accelerated expansion of the present Universe, significant theoretical developments have been made in the area of modified gravity. In the meantime, cosmological observations have been providing more high-quality data, allowing us to explore gravity on cosmological scales. To bridge the recent theoretical developments and observations, we present an overview of a variety of modified theories of gravity and the cosmological observables in the cosmic microwave background and large-scale structure, supplemented with a summary of predictions for cosmological observables derived from cosmological perturbations and sophisticated numerical studies. We specifically consider scalar-tensor theories in the Horndeski and DHOST family, massive gravity/bigravity, vector-tensor theories, metric-affine gravity, and cuscuton/minimally-modified gravity, and discuss the current status of those theories with emphasis on their physical motivations, validity, appealing features, the level of maturity, and calculability. We conclude that the Horndeski theory is one of the most well-developed theories of modified gravity, although several remaining issues are left for future observations. The paper aims to help to develop strategies for testing gravity with ongoing and forthcoming cosmological observations.

      DOI: 10.1093/ptep/ptad052

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    • CMB constraints on DHOST theories Peer-reviewed

      Takashi Hiramatsu

      Journal of Cosmology and Astroparticle Physics2022 ( 10 ) 035 - 035   1 10 2022

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      Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

      Abstract

      We put constraints on the degenerate higher-order scalar-tensor (DHOST) theories using the Planck 2018 likelihoods. In our previous paper, we developed a Boltzmann solver incorporating the effective field theory parameterised by the six time-dependent functions, α<sub>i</sub> (i =  B, K, T, M, H) and β<sub>1</sub>, which can describe the DHOST theories. Using the Markov-Chain Monte-Carlo method with our Boltzmann solver, we find the viable parameter region of the model parameters characterising the DHOST theories and the other standard cosmological parameters. First, we consider a simple model with α<sub></sub> = Ω<sub>DE</sub>(t)/Ω<sub>DE</sub>(t<sub>0</sub>), α<sub>B</sub> = α<sub>T</sub> = α<sub>M</sub> = α<sub>H</sub> = 0 and β<sub>1</sub> = β<sub>1,0</sub>Ω<sub>DE</sub>(t)/Ω<sub>DE</sub>(t<sub>0</sub>) in the ΛCDM background where t<sub>0</sub> is the present time and obtain β<sub>1,0</sub> = 0.032<sub>-0.016</sub><sup>+0.013</sup> (68% c.l.). Next, we focus on another theory given by ℒ<sub>DHOST</sub> = X + c<sub>3</sub>X□ϕ/Λ<sup>3</sup> + (M<sub>pl</sub><sup>2</sup>/2 + c<sub>4</sub>x<sup>2</sup>/Λ<sup>6</sup>)R + 48c<sub>4</sub><sup>2</sup>X<sup>2</sup>/ (M<sub>pl</sub><sup>2</sup>Λ<sup>12</sup> + 2c<sub>4</sub>Λ<sup>6</sup>X<sup>2</sup>)ϕ<sup>μ</sup>ϕ<sub>μρ</sub>ϕ<sup>ρν</sup>ϕ<sub>ν</sub> with X := ∂<sub>μ</sub>ϕ∂<sup>μ</sup>ϕ and two positive constant parameters, c<sub>3</sub> and c<sub>4</sub>. In this model, we consistently treat the background and the perturbations, and obtain c<sub>3</sub> = 1.59<sup>+0.26</sup><sub>-0.28</sub> and the upper bound on c<sub>4</sub>, c<sub>4</sub> &lt; 0.0088 (68% c.l.).

      DOI: 10.1088/1475-7516/2022/10/035

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      Other Link: https://iopscience.iop.org/article/10.1088/1475-7516/2022/10/035/pdf

    • Testing gravity with the cosmic microwave background: constraints on modified gravity with two tensorial degrees of freedom Peer-reviewed

      Takashi Hiramatsu, Tsutomu Kobayashi

      Journal of Cosmology and Astroparticle Physics2022 ( 07 ) 040 - 040   1 7 2022

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      Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

      Abstract

      We provide a cosmological test of modified gravity with two tensorial degrees of freedom and no extra propagating scalar mode. The theory of gravity we consider admits a cosmological model that is indistinguishable from the ΛCDM model at the level of the background evolution. The model has a single modified-gravity parameterβ, the effect of which can be seen in linear perturbations, though no extra scalar mode is propagating. Using the Boltzmann code modified to incorporate the present model, we derive the constraints -0.047 &lt;β&lt; -0.028 at 68% confidence from Planck CMB data. Since our modified gravity model can hardly be constrained by the Solar System tests and gravitational-wave propagation, our result offers the first observational test on the model.

      DOI: 10.1088/1475-7516/2022/07/040

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      Other Link: https://iopscience.iop.org/article/10.1088/1475-7516/2022/07/040/pdf

    • Gauge kinetic mixing and dark topological defects Peer-reviewed

      Takashi Hiramatsu, Masahiro Ibe, Motoo Suzuki, Soma Yamaguchi

      Journal of High Energy Physics2021 ( 12 ) 122 - 122   17 12 2021

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      Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

      Abstract

      We discuss how the topological defects in the dark sector affect the Standard Model sector when the dark photon has a kinetic mixing with the QED photon. In particular, we consider the dark photon appearing in the successive gauge symmetry breaking, SU(2)→U(1)→ ℤ<sub>2</sub>, where the remainingℤ<sub>2</sub>is the center of SU(2). In this model, the monopole is trapped into the cosmic strings and forms the so-called bead solution. As we will discuss, the dark cosmic string induces the QED magnetic flux inside the dark string through the kinetic mixing. The dark monopole, on the other hand, does not induce the QED magnetic flux in the U(1) symmetric phase, even in the presence of the kinetic mixing. Finally, we show that the dark bead solution induces a spherically symmetric QED magnetic flux through the kinetic mixing. The induced flux looks like the QED magnetic monopole viewed from a distance, although QED satisfies the Bianchi identity everywhere, which we call a pseudo magnetic monopole.

      DOI: 10.1007/jhep12(2021)122

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      Other Link: https://link.springer.com/article/10.1007/JHEP12(2021)122/fulltext.html

    • Gravitational wave spectra from oscillon formation after inflation Peer-reviewed

      Takashi Hiramatsu, Evangelos I. Sfakianakis, Masahide Yamaguchi

      Journal of High Energy Physics2021 ( 3 ) 021 - 021   2 3 2021

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      Authorship:Lead author   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

      Abstract

      We systematically investigate the preheating behavior of single field inflation with an oscillon-supporting potential. We compute both the properties of the emitted gravitational waves as well as the number density and characteristics of the produced oscillons. By performing numerical simulations for a variety of potential types, we divide the analyzed potentials in two families, each of them containing potentials with varying large- or small-field dependence. We find that the shape of the spectrum and the amplitude of emitted gravitational waves have a universal feature with the peak around the physical wavenumber k/a ∼ m at the inflaton oscillation starting period, irrespective of the exact potential shape. This can be used as a smoking-gun for deducing the existence of a violent preheating phase and possible oscillon formation after inflation. Despite this apparent universality, we also find differences in the shape of the spectrum of emitted gravitational waves between the two families of potentials, leading to discriminating features between them. In particular, all potentials show the emergence of a two-peak structure in the gravitational wave spectrum, arising at the time of oscillon formation. However, potentials that exhibit efficient parametric resonance tend to smear out this structure and by the end of the simulation the two-peak structure is replaced by one broad peak in the GW spectrum. We further compute the number density and properties of the produced oscillons for each potential choice, finding differences in the number density and size distribution of stable oscillons and transient overdensities. We also perform a linear fluctuation analysis and use the corresponding Floquet charts to relate the results of our simulations to the structure of parametric resonance for the various potential types. We find that the growth rate of the scalar perturbations and the associated oscillon formation time are sensitive to the small-field shape of a potential while the macroscopic physical properties of oscillons such as the total number depend on the large-field shape of a potential.

      DOI: 10.1007/jhep03(2021)021

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      Other Link: http://link.springer.com/article/10.1007/JHEP03(2021)021/fulltext.html

    • Statistically-anisotropic tensor bispectrum from inflation Peer-reviewed

      Takashi Hiramatsu, Kai Murai, Ippei Obata, Shuichiro Yokoyama

      Journal of Cosmology and Astroparticle Physics2021 ( 03 ) 047 - 047   1 3 2021

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

      Abstract

      We develop a possibility of generating tensor non-Gaussianity in a kind of anisotropic inflation, where a (1) gauge field is kinetically coupled to a spectator scalar field.Owing to this coupling, the coherent mode of the electric field appears and softly breaks the isotropy of the Universe.We compute the bispectrum of linearly-polarized tensor perturbations sourced by the gauge field and find that it is strongly red-tiltedand has distinctive statistical anisotropies including higher-order multipole moments.Interestingly, the tensor bispectra with the specific combinations of linear polarization modes are dominant, and their amplitudes depend on the different sets of multipole moments.This new type of statistically-anisotropic tensor non-Gaussianity can be potentially testable with the upcoming cosmic microwave background B-mode polarization experiments.

      DOI: 10.1088/1475-7516/2021/03/047

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      Other Link: https://iopscience.iop.org/article/10.1088/1475-7516/2021/03/047/pdf

    • Testing gravity theories with cosmic microwave background in the degenerate higher-order scalar-tensor theory Peer-reviewed

      Takashi Hiramatsu, Daisuke Yamauchi

      Physical Review D102 ( 8 ) 083525   19 10 2020

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      Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society (APS)  

      DOI: 10.1103/physrevd.102.083525

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      Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.102.083525/fulltext

    • Cosmic string in Abelian-Higgs model with enhanced symmetry — Implication to the axion domain-wall problem Peer-reviewed

      Takashi Hiramatsu, Masahiro Ibe, Motoo Suzuki

      Journal of High Energy Physics2020 ( 9 ) 054   9 2020

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      Authorship:Lead author   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

      <title>A<sc>bstract</sc>
      </title>
      In our previous work, we found new types of the cosmic string solutions in the Abelian-Higgs model with an enhanced U(1) global symmetry. We dubbed those solutions as the compensated/uncompensated strings. The compensated string is similar to the conventional cosmic string in the Abrikosov-Nielsen-Olesen (ANO) string, around which only the would-be Nambu-Goldstone (NG) boson winds. Around the uncompensated string, on the other hand, the physical NG boson also winds, where the physical NG boson is associated with the spontaneous breaking of the enhanced symmetry. Our previous simulation in the 2+1 dimensional spacetime confirmed that both the compensated/uncompensated strings are formed at the phase transition of the symmetry breaking. Non-trivial winding of the physical NG boson around the strings potentially causes the so-called axion domain- wall problem when the model is applied to the axion model. In this paper, we perform simulation in the 3+1 dimensional spacetime to discuss the fate of the uncompensated strings. We observe that the evolution of the string-network is highly complicated in the 3+1 dimensional simulation compared with that seen in the previous simulation. Despite such complications, we find that the number of the uncompensated strings which could cause can be highly suppressed at late times. Our observation suggests that the present setup can be applied to the axion model without suffering from the axion domain-wall problem.

      DOI: 10.1007/jhep09(2020)054

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      Other Link: http://link.springer.com/article/10.1007/JHEP09(2020)054/fulltext.html

    • New Type of String Solutions with Long Range Forces Peer-reviewed

      Takashi Hiramatsu, Masahiro Ibe, Motoo Suzuki

      Journal of High Energy Physics2002   058   2 2020

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      Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

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    • Testing Seesaw and Leptogenesis with Gravitational Waves Peer-reviewed

      Jeff A. Dror, Takashi Hiramatsu, Kazunori Kohri, Hitoshi Murayama, Graham White

      Physical Review Letters124   041804   8 8 2019

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      Language:English   Publishing type:Research paper (scientific journal)  

      We present the possibility that the seesaw mechanism with thermal
      leptogenesis can be tested using the stochastic gravitational background.
      Achieving neutrino masses consistent with atmospheric and solar neutrino data,
      while avoiding non-perturbative couplings, requires right-neutrinos lighter
      than the typical scale of grand unification. This scale separation suggests a
      symmetry protecting the right handed neutrinos from getting a mass. Thermal
      leptogenesis would then require that such a symmetry be broken below the
      reheating temperature. We enumerate all such possible symmetries consistent
      with these minimal assumptions and their corresponding defects, finding that in
      many cases, gravitational waves from the network of cosmic strings should be
      detectable. Estimating the predicted gravitational wave background we find that
      future space-borne missions could probe the entire range relevant for thermal
      leptogenesis.

      DOI: 10.1103/PhysRevLett.124.041804

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    • Hunting for Statistical Anisotropy in Tensor Modes with B-mode Observations Peer-reviewed

      Takashi Hiramatsu, Shuichiro Yokoyama, Tomohiro Fujita, Ippei Obata

        D98   083522   10 2018

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      Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

      We investigate a possibility of constraining statistical anisotropies of the<br />
      primordial tensor perturbations by using future observations for the Cosmic<br />
      Microwave Background (CMB) B-mode polarization. By parameterizing a<br />
      statistically-anisotropic tensor power spectrum as $P_h ({\boldsymbol{k } }) =<br />
      P_h (k) \sum_n g_n \cos^n \theta_{\boldsymbol{k } }$, where<br />
      $\theta_{\boldsymbol{k } }$ is an angle of the direction of<br />
      $\hat{k}={\boldsymbol{k } }/k$ from a preferred direction, we find that it would<br />
      be possible for future B-mode observations such as CMB-S4 to detect the tensor<br />
      statistical anisotropy at the level of $g_n \sim {\mathcal O} (0.1)$.

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    • Reconstruction of primordial tensor power spectra from B-mode polarization of the cosmic microwave background Peer-reviewed

      Takashi Hiramatsu, Eiichiro Komatsu, Masashi Hazumi, Misao Sasaki

      Physical ReviewD97   123511   6 2018

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      Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

      Given observations of B-mode polarization power spectrum of the cosmic microwave background (CMB), we can reconstruct power spectra of primordial tensor modes from the early Universe without assuming their functional form such as a power-law spectrum. Shape of the reconstructed spectra can then be used to probe the origin of tensor modes in a model-independent manner. We use the Fisher matrix to calculate the covariance matrix of tensor power spectra reconstructed in bins. We find that the power spectra are best reconstructed at wavenumbers in the vicinity of $k\approx 6\times 10^{-4}$ and $5\times 10^{-3}~{\rm Mpc}^{-1}$, which correspond to the &quot;reionization bump&quot; at $\ell\lesssim 6$ and &quot;recombination bump&quot; at $\ell\approx 80$ of the CMB B-mode power spectrum, respectively. The error bar between these two wavenumbers is larger because of lack of the signal between the reionization and recombination bumps. The error bars increase sharply towards smaller (larger) wavenumbers because of the cosmic variance (CMB lensing and instrumental noise). To demonstrate utility of the reconstructed power spectra we investigate whether we can distinguish between various sources of tensor modes including those from the vacuum metric fluctuation and SU(2) gauge fields during single-field slow-roll inflation, open inflation and massive gravity inflation. The results depend on the model parameters, but we find that future CMB experiments are sensitive to differences in these models. We make our calculation tool available on-line.

      DOI: 10.1103/PhysRevD.97.123511

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    • Relativistic stars in degenerate higher-order scalar-tensor theories after GW170817 Peer-reviewed

      Tsutomu Kobayashi, Takashi Hiramatsu

      Physical Review D97 ( 10 ) 104012   15 5 2018

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society  

      We study relativistic stars in degenerate higher-order scalar-tensor theories that evade the constraint on the speed of gravitational waves imposed by GW170817. It is shown that the exterior metric is given by the usual Schwarzschild solution if the lower order Horndeski terms are ignored in the Lagrangian and a shift symmetry is assumed. However, this class of theories exhibits partial breaking of Vainshtein screening in the stellar interior and thus modifies the structure of a star. Employing a simple concrete model, we show that for high-density stars the mass-radius relation is altered significantly even if the parameters are chosen so that only a tiny correction is expected in the Newtonian regime. We also find that, depending on the parameters, there is a maximum central density above which solutions cease to exist.

      DOI: 10.1103/PhysRevD.97.104012

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    • Anti-screening of the Galileon force around a disk center hole Peer-reviewed

      Hiromu Ogawa, Takashi Hiramatsu, Tsutomu Kobayashi

          14 2 2018

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      The Vainshtein mechanism is known as an efficient way of screening the fifth force around a matter source in modified gravity. This has been verified mainly in highly symmetric matter configurations. To study how the Vainshtein mechanism works in a less symmetric setup, we numerically solve the scalar field equation around a disk with a hole at its center in the cubic Galileon theory. We find, surprisingly, that the Galileon force is enhanced, rather than suppressed, in the vicinity of the hole. This anti-screening effect is larger for a thinner, less massive disk with a smaller hole. At this stage our setup is only of academic interest and its astrophysical consequences are unclear, but this result implies that the Vainshtein screening mechanism around less symmetric matter configurations is quite nontrivial.

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    • Y-junction intercommutations of current carrying strings Peer-reviewed

      D. A. Steer, Marc Lilley, Daisuke Yamauchi, Takashi Hiramatsu

      Physical Review D97 ( 2 )   10 1 2018

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society  

      Under certain conditions the collision and intercommutation of two cosmic strings can result in the formation of a third string, with the three strings then remaining connected at Y-junctions. The kinematics and dynamics of collisions of this type have been the subject of analytical and numerical analyses in the special case in which the strings are Nambu-Goto. Cosmic strings, however, may well carry currents, in which case their dynamics is not given by the Nambu-Goto action. Our aim is to extend the kinematic analysis to more general kinds of string model. We focus in particular on the collision of strings described by conservative elastic string models, characteristic of current carrying strings, and which are expected to form in a cosmological context. As opposed to Nambu-Goto strings collisions, we show that in this case the collision cannot lead to the formation of a third elastic string: if dynamically such a string forms then the joining string must be described by a more general equation of state. This process will be studied numerically in a forthcoming publication.

      DOI: 10.1103/PhysRevD.97.023507

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    • Space Gravitational Wave Antenna DECIGO and B-DECIGO

      Kawamura, Seiji, Nakamura, Takashi, Ando, Masaki, Seto, Naoki, Akutsu, Tomotada, Funaki, Ikkoh, Ioka, Kunihito, K, a, Nobuyuki, Kawano, Isao, Musha, Mitsuru, Nakazawa, Kazuhiro, Sato, Shuichi, Takashima, Takeshi, Tanaka, Takahiro, Tsubono, Kimio, Yokoyama, Jun'ichi, Agatsuma, Kazuhiro, Aoyanagi, Koh-suke, Arai, Koji, Araya, Akito, Aritomi, Naoki, Asada, Hideki, Aso, Yoichi, Chen, Dan, Chiba, Takeshi, Ebisuzaki, Toshikazu, Eguchi, Satoshi, Ejiri, Yumiko, Enoki, Motohiro, Eriguchi, Yoshiharu, Fujimoto, Masa-Katsu, Fujita, Ryuichi, Fukushima, Mitsuhiro, Futamase, Toshifumi, Gondo, Rina, Harada, Tomohiro, Hashimoto, Tatsuaki, Hayama, Kazuhiro, Hikida, Wataru, Himemoto, Yoshiaki, Hirabayashi, Hisashi, Hiramatsu, Takashi, Hong, Feng-Lei, Horisawa, Hideyuki, Hosokawa, Mizuhiko, Ichiki, Kiyotomo, Ikegami, Takeshi, Inoue, Kaiki T, Ishihara, Hideki, Ishikawa, Takehiko, Ishizaki, Hideharu, Ito, Hiroyuki, Itoh, Yousuke, Izumi, Kiwamu, Kanemura, Shinya, Kawashima, Nobuki, Kawazoe, Fumiko, Kishimoto, Naoko, Kiuchi, Kenta, Kobayashi, Shiho, Kohri, Kazunori, Koizumi, Hiroyuki, Kojima, Yasufumi, Kokeyama, Keiko, Kokuyama, Wataru, Kotake, Kei, Kozai, Yoshihide, Kunimori, Hiroo, Kuninaka, Hitoshi, Kuroda, Kazuaki, Kuroyanagi, Sachiko, Maeda, Kei-ichi, Matsuhara, Hideo, Matsumoto, Nobuyuki, Michimura, Yuta, Miyakawa, Osamu, Miyamoto, Umpei, Miyoki, Shinji, Morimoto, Mutsuko Y, Morisawa, Toshiyuki, Moriwaki, Shigenori, Mukohyama, Shinji, Nagano, Shigeo, Nakamura, Kouji, Nakano, Hiroyuki, Nakao, Kenichi, Nakasuka, Shinichi, Nakayama, Yoshinori, Nishida, Erina, Nishizawa, Atsushi, Niwa, Yoshito, Noumi, Taiga, Obuchi, Yoshiyuki, Ohishi, Naoko, Ohkawa, Masashi, Okada, Kenshi, Okada, Norio, Okutomi, Koki, Oohara, Kenichi, Sago, Norichika, Saijo, Motoyuki, Saito, Ryo, Sakagami, Masaaki, Sakai, Shin-ichiro, Sakata, Shihori, Sasaki, Misao, Sato, Takashi, Shibata, Masaru, Shibata, Kazunori, Shimo-oku, Ayumi, Shinkai, Hisaaki, Shoda, Ayaka, Somiya, Kentaro, Sotani, Hajime, Suemasa, Aru, Sugiyama, Naoshi, Suwa, Yudai, Suzuki, Rieko, Tagoshi, Hideyuki, Takahashi, Fuminobu, Takahashi, Kakeru, Takahashi, Keitaro, Takahashi, Ryutaro, Takahashi, Ryuichi, Takahashi, Hirotaka, Akiteru, Takamori, Takano, Tadashi, Tanaka, Nobuyuki, Taniguchi, Keisuke, Taruya, Atsushi, Tashiro, Hiroyuki, Torii, Yasuo, Toyoshima, Morio, Tsujikawa, Shinji, Ueda, Akitoshi, Ueda, Ken-ichi, Ushiba, Takafumi, Utashima, Masayoshi, Wakabayashi, Yaka, Yagi, Kent, Yamamoto, Kazuhiro, Yamazaki, Toshitaka, Yoo, Chul-Moon, Yoshida, Shijun, Yoshino, Taizoh

      International Journal of Modern Physics D0 ( ja )   2018

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      Publishing type:Research paper (scientific journal)  

      © 2018 World Scientific Publishing Company DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a future Japanese space gravitational-wave antenna. The most important objective of DECIGO, among various sciences to be aimed at, is to detect gravitational waves coming from the inflation of the universe. DECIGO consists of four clusters of spacecraft, and each cluster consists of three spacecraft with three Fabry–Perot Michelson interferometers. As a pathfinder mission of DECIGO, B-DECIGO will be launched, hopefully in the 2020s, to demonstrate technologies necessary for DECIGO as well as to lead to fruitful multimessenger astronomy. B-DECIGO is a small-scale or simpler version of DECIGO with the sensitivity slightly worse than that of DECIGO, yet good enough to provide frequent detection of gravitational waves.

      DOI: 10.1142/S0218271818450013

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    • The status of DECIGO Peer-reviewed

      Shuichi Sato, Seiji Kawamura, Masaki Ando, Takashi Nakamura, Kimio Tsubono, Akito Araya, Ikkoh Funaki, Kunihito Ioka, Nobuyuki Kanda, Shigenori Moriwaki, Mitsuru Musha, Kazuhiro Nakazawa, Kenji Numata, Shin Ichiro Sakai, Naoki Seto, Takeshi Takashima, Takahiro Tanaka, Kazuhiro Agatsuma, Koh Suke Aoyanagi, Koji Arai, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Yumiko Ejiri, Motohiro Enoki, Yoshiharu Eriguchi, Masa Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Katsuhiko Ganzu, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Nobuki Kawashima, Fumiko Kawazoe, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hideaki Kudoh, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei Ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Shinji Miyoki, Mutsuko Y. Morimoto, Tomoko Morioka, Toshiyuki Morisawa, Shinji Mukohyama, Shigeo Nagano, Isao Naito, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Taiga Noumi, Yoshiyuki Obuchi, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Norio Okada, Kouji Onozato, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Masaaki Sakagami, Shihori Sakata, Misao Sasaki

      Journal of Physics: Conference Series840 ( 1 )   1 6 2017

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      Language:English   Publishing type:Research paper (international conference proceedings)  

      © Published under licence by IOP Publishing Ltd. DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) is the planned Japanese space gravitational wave antenna, aiming to detect gravitational waves from astrophysically and cosmologically significant sources mainly between 0.1 Hz and 10 Hz and thus to open a new window for gravitational wave astronomy and for the universe. DECIGO will consists of three drag-free spacecraft arranged in an equilateral triangle with 1000 km arm lengths whose relative displacements are measured by a differential Fabry-Perot interferometer, and four units of triangular Fabry-Perot interferometers are arranged on heliocentric orbit around the sun. DECIGO is vary ambitious mission, we plan to launch DECIGO in era of 2030s after precursor satellite mission, B-DECIGO. B-DECIGO is essentially smaller version of DECIGO: B-DECIGO consists of three spacecraft arranged in an triangle with 100 km arm lengths orbiting 2000 km above the surface of the earth. It is hoped that the launch date will be late 2020s for the present..

      DOI: 10.1088/1742-6596/840/1/012010

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    • CMB scale dependent non-Gaussianity from massive gravity during inflation Peer-reviewed

      Domenech, Guillem, Hiramatsu, Takashi, Lin, Chunshan, Sasaki, Misao, Shiraishi, Maresuke, Wang, Yi

      Journal of Cosmology and Astroparticle Physics   2017

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      We consider a cosmological model in which the tensor mode becomes massive during inflation, and study the Cosmic Microwave Background (CMB) temperature and polarization bispectra arising from the mixing between the scalar mode and the massive tensor mode during inflation. The model assumes the existence of a preferred spatial frame during inflation. The local Lorentz invariance is already broken in cosmology due to the existence of a preferred rest frame. The existence of a preferred spatial frame further breaks the remaining local SO(3) invariance and in particular gives rise to a mass in the tensor mode. At linear perturbation level, we minimize our model so that the vector mode remains non-dynamical, while the scalar mode is the same as the one in single-field slow-roll inflation. At non-linear perturbation level, this inflationary massive graviton phase leads to a sizeable scalar-scalar-tensor coupling, much greater than the scalar-scalar-scalar one, as opposed to the conventional case. This scalar-scalar-tensor interaction imprints a scale dependent feature in the CMB temperature and polarization bispectra. Very intriguingly, we find a surprizing similarity between the predicted scale dependence and the scale-dependent non-Gaussianities at low multipoles hinted in the WMAP and Planck results.

      DOI: 10.1088/1475-7516/2017/05/034

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    • An update on the Axion Helioscopes front: Current activities at CAST and the IAXO project Peer-reviewed

      T. Dafni, M. Arik, E. Armengaud, S. Aune, F. T. Avignone, K. Barth, A. Belov, M. Betz, H. Bräuninger, P. Brax, N. Breijnholt, P. Brun, G. Cantatore, J. M. Carmona, G. P. Carosi, F. Caspers, S. Caspi, S. A. Cetin, D. Chelouche, F. E. Christensen, J. I. Collar, A. Dael, M. Davenport, A. V. Derbin, K. Desch, A. Diago, B. Döbrich, I. Dratchnev, A. Dudarev, C. Eleftheriadis, G. Fanourakis, E. Ferrer-Ribas, P. Friedrich, J. Galán, J. A. García, A. Gardikiotis, J. G. Garza, E. N. Gazis, E. Georgiopoulou, T. Geralis, B. Gimeno, I. Giomataris, S. Gninenko, H. Gómez, D. González-Díaz, E. Gruber, E. Guendelman, T. Guthörl, C. J. Hailey, R. Hartmann, S. Hauf, F. Haug, M. D. Hasinoff, T. Hiramatsu, D. H.H. Hoffmann, D. Horns, F. J. Iguaz, I. G. Irastorza, J. Isern, K. Imai, J. Jacoby, J. Jaeckel, A. C. Jakobsen, K. Jakovcić, J. Kaminski, M. Kawasaki, M. Karuza, K. Königsmann, R. Kotthaus, M. Krcmar, K. Kousouris, C. Krieger, M. Kuster, B. Lakić, J. M. Laurent, O. Limousin, A. Lindner, A. Liolios, A. Ljubicić, G. Luzón, S. Matsuki, V. N. Muratova, S. Neff, T. Niinikoski, C. Nones, I. Ortega, T. Papaevangelou, M. J. Pivovaroff, G. Raffelt, J. Redondo, H. Riege, A. Ringwald, A. Rodríguez, M. Rosu, S. Russenschuck, J. Ruz, K. Saikawa, I. Savvidis, T. Sekiguchi, Y. K. Semertzidis, I. Shilon, P. Sikivie, H. Silva, S. K. Solanki, L. Stewart, H. H.J. ten Kate, A. Tomas, S. Troitsky, T. Vafeiadis, K. van Bibber, P. Vedrine, J. A. Villar, J. K. Vogel, L. Walckiers, A. Weltman, W. Wester, S. C. Yildiz, K. Zioutas

      Nuclear and Particle Physics Proceedings273-275   244 - 249   1 4 2016

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:Elsevier  

      Although they have not yet been detected, axions and axion-like particles (ALPs) continue to maintain the interest (even increasingly so) of the rare-event searches community as viable candidates for the Dark Matter of the Universe but also as a solution for several other puzzles of astrophysics. Their property of coupling to photons has inspired different experimental methods for their detection, one of which is the helioscope technique. The CERN Axion Solar Telescope (CAST) is the most sensitive helioscope built up to date and has recently published part of the latest data taken with the magnet bores gradually filled with 3He, probing the mass range up to 1.17 eV. The International AXion Observatory (IAXO) is being proposed as a facility where different axion studies can be performed, with the primary goal to study axions coming from the Sun. Designed to maximize sensitivity, it will improve the levels reached by CAST by almost 5 orders of magnitude in signal detection, that is more than one order of magnitude in terms of ga γ. Here we will summarize the most important aspects of the helioscopes, and focus mainly on IAXO, based on the recent papers [1, 2].

      DOI: 10.1016/j.nuclphysbps.2015.09.033

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    • Reheating signature in the gravitational wave spectrum from self-ordering scalar fields Peer-reviewed

      Sachiko Kuroyanagi, Takashi Hiramatsu, Jun'ichi Yokoyama

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 2 )   2 2016

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      We investigate the imprint of reheating on the gravitational wave spectrum produced by self-ordering of multi-component scalar fields after a global phase transition. The equation of state of the Universe during reheating, which usually has different behaviour from that of a radiation-dominated Universe, affects the evolution of gravitational waves through the Hubble expansion term in the equations of motion. This gives rise to a different power-law behavior of frequency in the gravitational wave spectrum. The reheating history is therefore imprinted in the shape of the spectrum. We perform 512(3) lattice simulations to investigate how the ordering scalar field reacts to the change of the Hubble expansion and how the reheating effect arises in the spectrum. We also compare the result with inflation produced gravitational waves, which has a similar spectral shape, and discuss whether it is possible to distinguish the origin between inflation and global phase transition by detecting the shape with future direct detection gravitational wave experiments such as DECIGO.

      DOI: 10.1088/1475-7516/2016/02/023

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    • The IAXO Helioscope Peer-reviewed

      E Ferrer Ribas, E. Armengaud, F. T. Avignone, M. Betz, P. Brax, P. Brun, G. Cantatore, J. M. Carmona, G. P. Carosi, F. Caspers, S. Caspi, S. A. Cetin, D. Chelouche, F. E. Christensen, A. Dael, T. Dafni, M. Davenport, A. V. Derbin, K. Desch, A. Diago, B. Döbrich, I. Dratchnev, A. Dudarev, C. Eleftheriadis, G. Fanourakis, J. Galán, J. A. García, J. G. Garza, T. Geralis, B. Gimeno, I. Giomataris, S. Gninenko, H. Gómez, D. González-Diaz, E. Guendelman, C. J. Hailey, T. Hiramatsu, D. H.H. Hoffmann, D. Horns, F. J. Iguaz, I. G. Irastorza, J. Isern, K. Imai, J. Jaeckel, A. C. Jakobsen, K. Jakovčić, J. Kaminski, M. Kawasaki, M. Karuza, M. Krčmar, K. Kousouris, C. Krieger, B. Lakić, O. Limousin, A. Lindner, A. Liolios, G. Luzón, S. Matsuki, V. N. Muratova, C. Nones, I. Ortega, T. Papaevangelou, M. J. Pivovaroff, G. Raffelt, J. Redondo, A. Ringwald, S. Russenschuck, J. Ruz, K. Saikawa, I. Savvidis, T. Sekiguchi, Y. K. Semertzidis, I. Shilon, P. Sikivie, H. Silva, H. H.J. Ten Kate, A. Tomas, S. Troitsky, T. Vafeiadis, K. Van Bibber, P. Vedrine, J. A. Villar, J. K. Vogel, L. Walckiers, A. Weltman, W. Wester, S. C. Yildiz, K. Zioutas

      Journal of Physics: Conference Series650 ( 1 )   16 11 2015

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      Language:English   Publishing type:Research paper (international conference proceedings)   Publisher:Institute of Physics Publishing  

      The IAXO (International Axion Experiment) is a fourth generation helioscope with a sensitivity, in terms of detectable signal counts, at least 104 better than CAST phase-I, resulting in sensitivity on gaγ one order of magnitude better. To achieve this performance IAXO will count on a 8-coil toroidal magnet with 60 cm diameter bores and equipped with X-ray focusing optics into 0.20 cm2 spots coupled to ultra-low background Micromegas X-ray detectors. The magnet will be on a platform that will allow solar tracking for 12 hours per day. The next short term objectives are to prepare a Technical Design Report and to construct the first prototypes of the hardware main ingredients: demonstration coil, X-ray optics and low background detector while refining the physics case and studying the feasibility studies for Dark Matter axions.

      DOI: 10.1088/1742-6596/650/1/012009

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    • Effects of thermal fluctuations on thermal inflation Peer-reviewed

      Takashi Hiramatsu, Yuhei Miyamoto, Jun'ichi Yokoyama

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 3 )   3 2015

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

      The mechanism of thermal inflation, a relatively short period of accelerated expansion after primordial inflation, is a desirable ingredient for a certain class of particle physics models if they are not to be in contention with the cosmology of the early Universe. Though thermal inflation is most simply described in terms of a thermal effective potential, a thermal environment also gives rise to thermal fluctuations that must be taken into account. We numerically study the effects of these thermal fluctuations using lattice simulations. We conclude that though they do not ruin the thermal inflation scenario, the phase transition at the end of thermal inflation proceeds through phase mixing and is therefore not accompanied by the formations of bubbles nor appreciable amplitude of gravitational waves.

      DOI: 10.1088/1475-7516/2015/03/024

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    • The next generation of axion helioscopes: The International Axion Observatory (IAXO) Peer-reviewed

      J. K. Vogel, E. Armengaud, F. T. Avignone, M. Betz, P. Brax, P. Brun, G. Cantatore, J. M. Carmona, G. P. Carosi, F. Caspers, S. Caspi, S. A. Cetin, D. Chelouche, F. E. Christensen, A. Dael, T. Dafni, M. Davenport, A. V. Derbin, K. Desch, A. Diago, B. Doebrich, I. Dratchnev, A. Dudarev, C. Eleftheriadis, G. Fanourakis, E. Ferrer-Ribas, J. Galan, J. A. Garcia, J. G. Garza, T. Geralis, B. Gimeno, I. Giomataris, S. Gninenko, H. Gomez, D. Gonzalez-Diaz, E. Guendelman, C. J. Hailey, T. Hiramatsu, D. H. H. Hoffmann, D. Horns, F. J. Iguaz, I. G. Irastorza, J. Isern, K. Imai, A. C. Jakobsen, J. Jaeckel, K. Jakovcic, J. Kaminski, M. Kawasaki, M. Karuza, M. Krcmar, K. Kousouris, C. Krieger, B. Lakic, O. Limousin, A. Lindner, A. Liolios, G. Luzon, S. Matsuki, V. N. Muratova, C. Nones, I. Ortega, T. Papaevangelou, M. J. Pivovaroff, G. Raffelt, J. Redondo, A. Ringwald, S. Russenschuck, J. Ruz, K. Saikawa, I. Savvidis, T. Sekiguchi, Y. K. Semertzidis, I. Shilon, P. Sikivie, H. Silva, H. ten Kate, A. Tomas, S. Troitsky, T. Vafeiadis, K. van Bibber, P. Vedrine, J. A. Villar, L. Walckiers, A. Weltman, W. Wester, S. C. Yildiz, K. Zioutas

      13TH INTERNATIONAL CONFERENCE ON TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS, TAUP 201361   193 - 200   2015

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      Language:English   Publishing type:Research paper (international conference proceedings)   Publisher:ELSEVIER SCIENCE BV  

      The International Axion Observatory (IAXO) is a proposed 4th-generation axion helioscope with the primary physics research goal to search for solar axions via their Primakoff conversion into photons of 1 - 10 keV energies in a strong magnetic field. IAXO will achieve a sensitivity to the axion-photon coupling ga. down to a few x10(-12) GeV-1 for a wide range of axion masses up to similar to 0.25 eV. This is an improvement over the currently best (3rd generation) axion helioscope, the CERN Axion Solar Telescope (CAST), of about 5 orders of magnitude in signal strength, corresponding to a factor similar to 20 in the axion photon coupling. IAXO's sensitivity relies on the construction of a large superconducting 8-coil toroidal magnet of 20 m length optimized for axion research. Each of the eight 60 cm diameter magnet bores is equipped with x-ray optics focusing the signal photons into similar to 0.2 cm(2) spots that are imaged by very low background x-ray detectors. The magnet will be built into a structure with elevation and azimuth drives that will allow solar tracking for 12 hours each day. This contribution is a summary of our papers [1, 2, 3] and we refer to these for further details. (C) 2015 The Authors. Published by Elsevier B.V.

      DOI: 10.1016/j.phpro.2014.12.031

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    • Regularized cosmological power spectrum and correlation function in modified gravity models Peer-reviewed

      Atsushi Taruya, Takahiro Nishimichi, Francis Bernardeau, Takashi Hiramatsu, Kazuya Koyama

      PHYSICAL REVIEW D90 ( 12 )   12 2014

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

      Based on the multipoint propagator expansion, we present resummed perturbative calculations for cosmological power spectra and correlation functions in the context of modified gravity. In a wide class of modified gravity models that have a screening mechanism to recover general relativity (GR) on small scales, we apply the eikonal approximation to derive the governing equation for resummed propagator that partly includes the nonperturbative effect in the high-k limit. The resultant propagator in the high-k limit contains the new corrections arising from the screening mechanism as well as the standard exponential damping. We explicitly derive the expression for new high-k contributions in specific modified gravity models, and find that in the case of f(R) gravity for a currently constrained model parameter, the corrections are basically of the subleading order and can be neglected. Thus, in f(R) gravity, similarly to the GR case, we can analytically construct the regularized propagator that reproduces both the resummed high-k behavior and the low-k results computed with standard perturbation theory, consistently taking account of the nonlinear modification of gravity valid at large scales. With the regularized multipoint propagators, we give predictions for power spectrum and correlation function at one-loop order, and compare those with N-body simulations in f(R) gravity model. As an important application, we also discuss the redshift-space distortions and compute the anisotropic power spectra and correlation functions.

      DOI: 10.1103/PhysRevD.90.123515

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    • Geodesic curve-of-sight formulae for the cosmic microwave background: a unified treatment of redshift, time delay, and lensing Peer-reviewed

      Ryo Saito, Atsushi Naruko, Takashi Hiramatsu, Misao Sasaki

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 10 )   10 2014

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

      In this paper, we introduce a new approach to a treatment of the gravitational effects (redshift, time delay and lensing) on the observed cosmic microwave background (CMB) anisotropies based on the Boltzmann equation. From the Liouville's theorem in curved space-time, the intensity of photons is conserved along a photon geodesic when non-gravitational scatterings are absent. Motivated by this fact, we derive a second-order line-of-sight formula by integrating the Boltzmann equation along a perturbed geodesic (curve) instead of a background geodesic (line). In this approach, the separation of the gravitational and intrinsic effects are manifest. This approach can be considered as a generalization of the remapping approach of CMB lensing, where all the gravitational effects can be treated on the same footing.

      DOI: 10.1088/1475-7516/2014/10/051

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    • Conceptual design of the International Axion Observatory (IAXO) Peer-reviewed

      E. Armengaud, F. T. Avignone, M. Betz, P. Brax, P. Brun, G. Cantatore, J. M. Carmona, G. P. Carosi, F. Caspers, S. Caspi, S. A. Cetin, D. Chelouche, F. E. Christensen, A. Dael, T. Dafni, M. Davenport, A. V. Derbin, K. Desch, A. Diago, B. Doebrich, I. Dratchnev, A. Dudarev, C. Eleftheriadis, G. Fanourakis, E. Ferrer-Ribas, J. Galan, J. A. Garcia, J. G. Garza, T. Geralis, B. Gimeno, I. Giomataris, S. Gninenko, H. Gomez, D. Gonzalez-Diaz, E. Guendelman, C. J. Hailey, T. Hiramatsu, D. H. H. Hoffmann, D. Horns, F. J. Iguaz, I. G. Irastorza, J. Isern, K. Imai, A. C. Jakobsen, J. Jaeckel, K. Jakovcic, J. Kaminski, M. Kawasaki, M. Karuza, M. Krcmar, K. Kousouris, C. Krieger, B. Lakic, O. Limousin, A. Lindner, A. Liolios, G. Luzon, S. Matsuki, V. N. Muratova, C. Nones, I. Ortega, T. Papaevangelou, M. J. Pivovaroff, G. Raffelt, J. Redondo, A. Ringwald, S. Russenschuck, J. Ruz, K. Saikawa, I. Savvidis, T. Sekiguchi, Y. K. Semertzidis, I. Shilon, P. Sikivie, H. Silva, H. ten Kate, A. Tomas, S. Troitsky, T. Vafeiadis, K. van Bibber, P. Vedrine, J. A. Villar, J. K. Vogel, L. Walckiers, A. Weltman, W. Wester, S. C. Yildiz, K. Zioutas

      JOURNAL OF INSTRUMENTATION9   5 2014

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

      The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, TAX will look for axions or axion-like particles (ALPs) originating in the Sun via the Primakoff conversion of the solar plasma photons. In terms of signalto-noise ratio, TAX will be about 4-5 orders of magnitude more sensitive than CAST, currently the most powerful axion helioscope, reaching sensitivity to axion-photon couplings down to a few x 10-12 GeV-1 and thus probing a large fraction of the currently unexplored axion and ALP parameter space. TAX will also be sensitive to solar axions produced by mechanisms mediated by the axion-electron coupling ga, with sensitivity for the first time to values of ga, not previously excluded by astrophysics. With several other possible physics cases, TAX has the potential to serve as a multi-purpose facility for generic axion and ALP research in the next decade. In this paper we present the conceptual design of IAXO, which follows the layout of an enhanced axion helioscope, based on a purpose-built 20 m-long 8-coils toroidal superconducting magnet. All the eight 60cm-diameter magnet bores are equipped with focusing x-ray optics, able to focus the signal photons into similar to 0.2 cm(2) spots that are imaged by ultra-low-background Micromegas x-ray detectors. The magnet is built into a structure with elevation and azimuth drives that will allow for solar tracking for similar to 12 h each day.

      DOI: 10.1088/1748-0221/9/05/T05002

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    • On the estimation of gravitational wave spectrum from cosmic domain walls Peer-reviewed

      Takashi Hiramatsu, Masahiro Kawasaki, Ken'ichi Saikawa

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 2 )   2 2014

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

      We revisit the production of gravitational waves from unstable domain walls analyzing their spectrum by the use of field theoretic lattice simulations with grid size 10243, which is larger than the previous study. We have recognized that there exists an error in the code used in the previous study, and the correction of the error leads to the suppression of the spectrum of gravitational waves at high frequencies. The peak of the spectrum is located at the scale corresponding to the Hubble radius at the time of the decay of domain walls, and its amplitude is consistent with the naive estimation based On the quadrupole formula. Using the numerical results, the magnitude and the peak frequency of gravitational waves at the present time are estimated. It is shown that for some choices of parameters the signal of gravitational waves is strong enough to be probed in the future gravitational wave experiments.

      DOI: 10.1088/1475-7516/2014/02/031

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    • Beyond consistency test of gravity with redshift-space distortions at quasilinear scales Peer-reviewed

      Atsushi Taruya, Kazuya Koyama, Takashi Hiramatsu, Akira Oka

      PHYSICAL REVIEW D89 ( 4 )   2 2014

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

      Redshift-space distortions (RSDs) offer an attractive method to measure the growth of cosmic structure on large scales, and combining with the measurement of the cosmic expansion history, they can be used as cosmological tests of gravity. With the advent of future galaxy redshift surveys aiming at precisely measuring the RSD, an accurate modeling of RSD going beyond linear theory is a critical issue in order to detect or disprove small deviations from general relativity (GR). While several improved models of RSD have been recently proposed based on the perturbation theory (PT), the framework of these models heavily relies on GR. Here, we put forward a new PT prescription for RSD in general modified gravity models. As a specific application, we present theoretical predictions of the redshift-space power spectra in the f(R) gravity model, and compare them with N-body simulations. Using the PT template that takes into account the effects of both modifications of gravity and RSD properly, we successfully recover the fiducial model parameter in N-body simulations in an unbiased way. On the other hand, we found it difficult to detect the scale dependence of the growth rate in a model-independent way based on GR templates.

      DOI: 10.1103/PhysRevD.89.043509

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    • Instability of colliding metastable strings Peer-reviewed

      Takashi Hiramatsu, Minoru Eto, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi

      JOURNAL OF HIGH ENERGY PHYSICS ( 1 )   1 2014

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER  

      The breaking of U(1) R symmetry plays a crucial role in modeling the breaking of supersymmetry (SUSY). In the models that possess both SUSY preserving and SUSY breaking vacua, tube-like cosmic strings called R-tubes, whose surfaces are constituted by domain walls interpolating a false and a true vacuum with some winding numbers, can exist. Their (in) stability can strongly constrain SUSY breaking models theirselves. In the present study, we investigate the dynamical (in) stability of two colliding metastable tube-like strings by field-theoretic simulations. From them, we find that the strings become unstable, depending on the relative collision angle and speed of two strings, and the false vacuum is eventually filled out by the true vacuum owing to rapid expansion of the strings or unstable bubbles created as remnants of the collision.

      DOI: 10.1007/JHEP01(2014)165

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    • Production and Evolution of Dark Matter Axions in the Early Universe

      Ken’ichi Saikawa, Takashi Hiramatsu, Masahiro Kawasaki, Toshifumi Noumi, Ryosuke Sato, Toyokazu Sekiguchi, Masahide Yamaguchi

      Proceedings in 10th Patras workshop on Axions, WIMPs and WISPs (axion-wimp2014)   2014

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    • Type-I cosmic-string network Peer-reviewed

      Takashi Hiramatsu, Yuuiti Sendouda, Keitaro Takahashi, Daisuke Yamauchi, Chul-Moon Yoo

      PHYSICAL REVIEW D88 ( 8 )   10 2013

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

      We study the network of Type-I cosmic strings using the field-theoretic numerical simulations in the Abelian-Higgs model. For Type-I strings, the gauge field plays an important role, and thus we find that the correlation length of the strings is strongly dependent upon the parameter beta the ratio between the masses of the scalar field and the gauge field, namely, beta = m(phi)(2)/m(A)(2). In particular, if we take the cosmic expansion into account, the network becomes densest in the comoving box for a specific value of beta for beta &lt; 1.

      DOI: 10.1103/PhysRevD.88.085021

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    • Equivalence principle violation in Vainshtein screened two-body systems Peer-reviewed

      Takashi Hiramatsu, Wayne Hu, Kazuya Koyama, Fabian Schmidt

      Physical Review D - Particles, Fields, Gravitation and Cosmology87 ( 6 )   26 3 2013

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      In massive gravity, galileon, and braneworld explanations of cosmic acceleration, force modifications are screened by nonlinear derivative self-interactions of the scalar field mediating that force. Interactions between the field of a central body ("A") and an orbiting body ("B") imply that body B does not move as a test body in the field of body A if the orbit is smaller than the Vainshtein radius of body B. We find through numerical solutions of the joint field at the position of B that the A-field Laplacian is nearly perfectly screened by the B self-field, whereas first derivative or net forces are reduced in a manner that scales with the mass ratio of the bodies as (MB/MA)3/5. The latter causes mass-dependent reductions in the universal perihelion precession rate due to the fifth force, with deviations for the Earth-Moon system at the ∼4% level. In spite of universal coupling, which preserves the microscopic equivalence principle, the motion of macroscopic screened bodies depends on their mass providing in principle a means for testing the Vainshtein mechanism. © 2013 American Physical Society.

      DOI: 10.1103/PhysRevD.87.063525

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    • Equivalence principle violation in Vainshtein screened two-body systems Peer-reviewed

      Takashi Hiramatsu, Wayne Hu, Kazuya Koyama, Fabian Schmidt

      PHYSICAL REVIEW D87 ( 6 )   3 2013

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

      In massive gravity, galileon, and braneworld explanations of cosmic acceleration, force modifications are screened by nonlinear derivative self-interactions of the scalar field mediating that force. Interactions between the field of a central body ("A'') and an orbiting body ("B'') imply that body B does not move as a test body in the field of body A if the orbit is smaller than the Vainshtein radius of body B. We find through numerical solutions of the joint field at the position of B that the A-field Laplacian is nearly perfectly screened by the B self-field, whereas first derivative or net forces are reduced in a manner that scales with the mass ratio of the bodies as (M-B/M-A)(3/5). The latter causes mass-dependent reductions in the universal perihelion precession rate due to the fifth force, with deviations for the Earth-Moon system at the similar to 4% level. In spite of universal coupling, which preserves the microscopic equivalence principle, the motion of macroscopic screened bodies depends on their mass providing in principle a means for testing the Vainshtein mechanism. DOI: 10.1103/PhysRevD.87.063525

      DOI: 10.1103/PhysRevD.87.063525

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    • Axion cosmology with long-lived domain walls Peer-reviewed

      Takashi Hiramatsu, Masahiro Kawasaki, Ken'ichi Saikawa, Toyokazu Sekiguchi

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 1 )   1 2013

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

      We investigate the cosmological constraints on axion models where the domain wall number is greater than one. In these models, multiple domain walls attached to strings are formed, and they survive for a long time. Their annihilation occurs due to the effects of explicit symmetry breaking term which might be raised by Planck-scale physics. We perform three-dimensional lattice simulations and compute the spectra of axions and gravitational waves produced by long-lived domain walls. Using the numerical results, we estimated relic density of axions and gravitational waves. We find that the existence of long-lived domain walls leads to the overproduction of cold dark matter axions, while the density of gravitational waves is too small to observe at the present time. Combining the results with other observational constraints, we find that the whole parameter region of models are excluded unless an unacceptable fine-tuning exists.

      DOI: 10.1088/1475-7516/2013/01/001

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    • “Cosmological Upper-Bound for f(R) gravity through redshift-space distortion”

      O. K.A. Akira, Atsushi Taruya, Takashi Hiramatsu, Kazuya Koyama, Kazuhiro Yamamoto, Takahiro Nishimichi

      JGRG 2013 - Proceedings of the 23rd Workshop on General Relativity and Gravitation in Japan2   427 - 437   2013

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      Sample: SDSS LRG (P0,P2) @ z = 0.3 Model: Perturbation Theory fR0 < 1.5*10-4 Cosmic Expansion & fR0 With More General Gravity Model With More Refined Galaxy Samples; SDSS-III BOSS, Subaru PFS (Upcoming)... etc.

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    • Future axion searches with the International Axion Observatory (IAXO) Peer-reviewed

      I. G. Irastorza, F. T. Avignone, G. Cantatore, J. M. Carmona, S. Caspi, S. A. Cetin, F. E. Christensen, A. Dael, T. Dafni, M. Davenport, A. V. Derbin, K. Desch, A. Diago, B. Doebrich, A. Dudarev, C. Eleftheriadis, G. Fanourakis, E. Ferrer-Ribas, J. Galan, J. A. Garcia, J. G. Garza, T. Geralis, B. Gimeno, I. Giomataris, S. Gninenko, H. Gomez, E. Guendelman, C. J. Hailey, T. Hiramatsu, D. H. H. Hoffmann, D. Horns, F. J. Iguaz, J. Isern, A. C. Jakobsen, J. Jaeckel, K. Jakovcic, J. Kaminski, M. Kawasaki, M. Krcmar, C. Krieger, B. Lakic, A. Lindner, A. Liolios, G. Luzon, I. Ortega, T. Papaevangelou, M. J. Pivovaroff, G. Raffelt, J. Redondo, A. Ringwald, S. Russenschuck, J. Ruz, K. Saikawa, I. Savvidis, T. Sekiguchi, I. Shilon, P. Sikivie, H. Silva, H. ten Kate, A. Tomas, S. Troitsky, T. Vafeiadis, K. van Bibber, P. Vedrine, J. A. Villar, J. K. Vogel, L. Walckiers, W. Wester, S. C. Yildiz, K. Zioutas

      SIXTH SYMPOSIUM ON LARGE TPCS FOR LOW ENERGY RARE EVENT DETECTION460   2013

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      The International Axion Observatory (IAXO) is a new generation axion helioscope aiming at a sensitivity to the axion-photon coupling of g(alpha gamma) greater than or similar to few x 10(-12) GeV-1, i.e. 1-1.5 orders of magnitude beyond the one achieved by CAST, currently the most sensitive axion helioscope. The main elements of IAXO are an increased magnetic field volume together with extensive use of x-ray focusing optics and low background detectors, innovations already successfully tested in CAST. Additional physics cases of IAXO could include the detection of electron-coupled axions invoked to explain the white dwarf cooling, relic axions, and a large variety of more generic axion-like particles (ALPs) and other novel excitations at the low-energy frontier of elementary particle physics.

      DOI: 10.1088/1742-6596/460/1/012002

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    • Production of dark matter axions from collapse of string-wall systems (vol 85, 105020, 2012) Peer-reviewed

      Takashi Hiramatsu, Masahiro Kawasaki, Ken'ichi Saikawa, Toyokazu Sekiguchi

      PHYSICAL REVIEW D86 ( 8 )   10 2012

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      We analyze the spectrum of axions radiated from collapse of domain walls, which have received less attention in the literature. The evolution of topological defects related to the axion models is investigated by performing field-theoretic lattice simulations. We simulate the whole process of evolution of the defects, including the formation of global strings, the formation of domain walls and the annihilation of the defects due to the tension of walls. The spectrum of radiated axions has a peak at the low frequency, which implies that axions produced by the collapse of domain walls are not highly relativistic. We revisit the relic abundance of cold dark matter axions and find that the contribution from the decay of defects can be comparable with the contribution from strings. This result leads to a more severe upper bound on the axion decay constant.

      DOI: 10.1103/PhysRevD.86.089902

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    • Production of dark matter axions from collapse of string-wall systems Peer-reviewed

      Takashi Hiramatsu, Masahiro Kawasaki, Ken'ichi Saikawa, Toyokazu Sekiguchi

      PHYSICAL REVIEW D85 ( 10 )   5 2012

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      We analyze the spectrum of axions radiated from collapse of domain walls, which have received less attention in the literature. The evolution of topological defects related to the axion models is investigated by performing field-theoretic lattice simulations. We simulate the whole process of evolution of the defects, including the formation of global strings, the formation of domain walls, and the annihilation of the defects due to the tension of walls. The spectrum of radiated axions has a peak at the low frequency, which implies that axions produced by the collapse of domain walls are not highly relativistic. We revisit the relic abundance of cold dark matter axions and find that the contribution from the decay of defects can be comparable with the contribution from strings. This result leads to a more severe upper bound on the axion decay constant.

      DOI: 10.1103/PhysRevD.85.105020

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    • Evolution of string-wall networks and axionic domain wall problem Peer-reviewed

      Takashi Hiramatsu, Masahiro Kawasaki, Ken'ichi Saikawa

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 8 )   8 2011

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      We study the cosmological evolution of domain walls bounded by strings which arise naturally in axion models. If we introduce a bias in the potential, walls become metastable and finally disappear. We perform two dimensional lattice simulations of domain wall networks and estimate the decay rate of domain walls. By using the numerical results, we give a constraint for the bias parameter and the Peccei-Quinn scale. We also discuss the possibility to probe axion models by direct detection of gravitational waves produced by domain walls.

      DOI: 10.1088/1475-7516/2011/08/030

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    • Improved estimation of radiated axions from cosmological axionic strings Peer-reviewed

      Takashi Hiramatsu, Masahiro Kawasaki, Toyokazu Sekiguchi, Masahide Yamaguchi, Jun&apos;ichi Yokoyama

      PHYSICAL REVIEW D83 ( 12 )   6 2011

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      Cosmological evolution of axionic string network is analyzed in terms of field-theoretic simulations in a box of 512(3) grids, which are the largest ever, using a new and more efficient identification scheme of global strings. The scaling parameter is found to be xi = 0.87 +/- 0.14 in agreement with previous results. The energy spectrum is calculated precisely using a pseudo power spectrum estimator which significantly reduces the error in the mean reciprocal comoving momentum. The resultant constraint on the axion decay constant leads to f(a) &lt;= 3 x 10(11) GeV. We also discuss implications for the early Universe.

      DOI: 10.1103/PhysRevD.83.123531

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    • The Japanese space gravitational wave antenna: DECIGO Peer-reviewed

      Seiji Kawamura, Masaki Ando, Naoki Seto, Shuichi Sato, Takashi Nakamura, Kimio Tsubono, Nobuyuki Kanda, Takahiro Tanaka, Jun'ichi Yokoyama, Ikkoh Funaki, Kenji Numata, Kunihito Ioka, Takeshi Takashima, Kazuhiro Agatsuma, Tomotada Akutsu, Koh-suke Aoyanagi, Koji Arai, Akito Araya, Hideki Asada, Yoichi Aso, Dan Chen, Takeshi Chiba, Toshikazu Ebisuzaki, Yumiko Ejiri, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Kiwamu Izumi, Isao Kawano, Nobuki Kawashima, Fumiko Kawazoe, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Sachiko Kuroyanagi, Kei-ichi Maeda, Hideo Matsuhara, Nobuyuki Matsumoto, Yuta Michimura, Osamu Miyakawa, Umpei Miyamoto, Shinji Miyoki, Mutsuko Y. Morimoto, Toshiyuki Morisawa, Shigenori Moriwaki, Shinji Mukohyama, Mitsuru Musha, Shigeo Nagano, Isao Naito, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Kazuhiro Nakazawa, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Taiga Noumi, Yoshiyuki Obuchi, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Kenshi Okada, Norio Okada, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Ryo Saito, Masaaki Sakagami, Shin-ichiro Sakai, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Ayaka Shoda, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Rieko Suzuki, Hideyuki Tagoshi, Fuminobu Takahashi, Kakeru Takahashi, Keitaro Takahashi, Ryutaro Takahashi, Ryuichi Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Takamori Akiteru, Tadashi Takano, Nobuyuki Tanaka, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Yasuo Torii, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Akitoshi Ueda, Ken-ichi Ueda, Masayoshi Utashima, Yaka Wakabayashi, Kent Yagi, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino, Ke-Xun Sun

      CLASSICAL AND QUANTUM GRAVITY28 ( 9 )   5 2011

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      The objectives of the DECi-hertz Interferometer Gravitational Wave Observatory (DECIGO) are to open a new window of observation for gravitational wave astronomy and to obtain insight into significant areas of science, such as verifying and characterizing inflation, determining the thermal history of the universe, characterizing dark energy, describing the formation mechanism of supermassive black holes in the center of galaxies, testing alternative theories of gravity, seeking black hole dark matter, understanding the physics of neutron stars and searching for planets around double neutron stars. DECIGO consists of four clusters of spacecraft in heliocentric orbits; each cluster employs three drag-free spacecraft, 1000 km apart from each other, whose relative displacements are measured by three pairs of differential Fabry-Perot Michelson interferometers. Two milestone missions, DECIGO pathfinder and Pre-DECIGO, will be launched to demonstrate required technologies and possibly to detect gravitational waves.

      DOI: 10.1088/0264-9381/28/9/094011

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    • Numerical Study of Q-Ball Formation in Gravity Mediation Peer-reviewed

      Takashi Hiramatsu, Masahiro Kawasaki, Fuminobu Takahashi

      PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT ( 190 ) 229 - 238   2011

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      We study Q-ball formation in the expanding universe on 3D lattice simulations. We obtain detailed Q-ball charge distributions, and find that the distribution is peaked at Q(peak)(3D) similar or equal to 1.9 x 10(-2)(vertical bar Phi(in)vertical bar/m)(2), which is greater than the existing result by about 60%. Based on the numerical simulations, we discuss how the Q-ball formation proceeds. Also we make a comment on possible deviation of the charge distributions from what was conjectured in the past.

      DOI: 10.1088/1475-7516/2010/06/008

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    • Numerical study of Q-ball formation in gravity mediation Peer-reviewed

      Takashi Hiramatsu, Masahiro Kawasaki, Fuminobu Takahashi

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 6 )   6 2010

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      We study Q-ball formation in the expanding universe on 1D, 2D and 3D lattice simulations. We obtain detailed Q-ball charge distributions, and find that the distribution is peaked at Q(peak)(3D) similar or equal to 1.9 x 10(-2) (vertical bar Phi(in)vertical bar/m)(2), which is greater than the existing result by about 60%. Based on the numerical simulations, we discuss how the Q-ball formation proceeds. Also we make a comment on possible deviation of the charge distributions from what was conjectured in the past.

      DOI: 10.1088/1475-7516/2010/06/008

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    • Gravitational waves from collapsing domain walls Peer-reviewed

      Takashi Hiramatsu, Masahiro Kawasaki, Ken'ichi Saikawa

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 5 )   5 2010

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      We study the production of gravitational waves from cosmic domain walls created during phase transition in the early universe. We investigate the process of formation and evolution of domain walls by running three dimensional lattice simulations. If we introduce an approximate discrete symmetry, walls become metastable and finally disappear. This process might occur by a pressure difference between two vacua if a quantum tunneling is neglected. We calculate the spectrum of gravitational waves produced by collapsing metastable domain walls. Extrapolating the numerical results, we find that the signal of gravitational waves produced by domain walls whose energy scale is around 10(10)-10(12)GeV will be observable in the next generation gravitational wave interferometers.

      DOI: 10.1088/1475-7516/2010/05/032

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    • DECIGO and DECIGO pathfinder Peer-reviewed

      Masaki Ando, Seiji Kawamura, Naoki Seto, Shuichi Sato, Takashi Nakamura, Kimio Tsubono, Takeshi Takashima, Ikkoh Funaki, Kenji Numata, Nobuyuki Kanda, Takahiro Tanaka, Kunihito Ioka, Kazuhiro Agatsuma, Koh-suke Aoyanagi, Koji Arai, Akito Araya, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Yumiko Ejiri, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Kiwamu Izumi, Isao Kawano, Nobuki Kawashima, Fumiko Kawazoe, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei-ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Umpei Miyamoto, Shinji Miyoki, Mutsuko Y. Morimoto, Toshiyuki Morisawa, Shigenori Moriwaki, Shinji Mukohyama, Mitsuru Musha, Shigeo Nagano, Isao Naito, Kouji Nakamura, Masahiro Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Kazuhiro Nakazawa, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Taiga Noumi, Yoshiyuki Obuchi, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Kenshi Okada, Norio Okada, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Ryo Saito, Masaaki Sakagami, Shin-ichiro Sakai, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Rieko Suzuki, Hideyuki Tagoshi, Fuminobu Takahashi, Kakeru Takahashi, Keitaro Takahashi, Ryutaro Takahashi, Ryuichi Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Takamori Akiteru, Tadashi Takano, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Yasuo Torii, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Akitoshi Ueda, Ken-ichi Ueda, Masayoshi Utashima, Yaka Wakabayashi, Kent Yagi, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Jun'ichi Yokoyama, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino, Ken-Xun Sun

      CLASSICAL AND QUANTUM GRAVITY27 ( 8 )   4 2010

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      A space gravitational-wave antenna, DECIGO (DECI-hertz interferometer Gravitational wave Observatory), will provide fruitful insights into the universe, particularly on the formation mechanism of supermassive black holes, dark energy and the inflation of the universe. In the current pre-conceptual design, DECIGO will be comprising four interferometer units; each interferometer unit will be formed by three drag-free spacecraft with 1000 km separation. Since DECIGO will be an extremely challenging mission with high-precision formation flight with long baseline, it is important to increase the technical feasibility before its planned launch in 2027. Thus, we are planning to launch two milestone missions. DECIGO pathfinder (DPF) is the first milestone mission, and key components for DPF are being tested on ground and in orbit. In this paper, we review the conceptual design and current status of DECIGO and DPF.

      DOI: 10.1088/0264-9381/27/8/084010

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    • Nonlinear evolution of baryon acoustic oscillations from improved perturbation theory in real and redshift spaces Peer-reviewed

      Atsushi Taruya, Takahiro Nishimichi, Shun Saito, Takashi Hiramatsu

      PHYSICAL REVIEW D80 ( 12 )   12 2009

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      We study the nonlinear evolution of baryon acoustic oscillations in the matter power spectrum and correlation function from the improved perturbation theory (PT). Based on the framework of renormalized PT, which provides a nonperturbative way to treat the gravitational clustering of large-scale structure, we apply the closure approximation that truncates the infinite series of loop contributions at one-loop order, and obtain a closed set of integral equations for power spectrum and nonlinear propagator. The resultant integral expressions are basically equivalent to those previously derived in the form of evolution equations, and they keep important nonperturbative properties which can dramatically improve the prediction of nonlinear power spectrum. Employing the Born approximation, we then derive the analytic expressions for nonlinear power spectrum and the predictions are made for nonlinear evolution of baryon acoustic oscillations in power spectrum and correlation function. We find that the improved PT possesses a better convergence property compared with standard PT calculation. A detailed comparison between improved PT results and N-body simulations shows that a percent-level agreement is achieved in a certain range in power spectrum and in a rather wider range in correlation function. Combining a model of nonlinear redshift-space distortion, we also evaluate the power spectrum and correlation function in redshift space. In contrast to the results in real space, the agreement between N-body simulations and improved PT predictions tends to be worse, and a more elaborate modeling for redshift-space distortion needs to be developed. Nevertheless, with the currently existing model, we find that the prediction of correlation function has a sufficient accuracy compared with the cosmic-variance errors for future galaxy surveys with volume of a few h(-3) Gpc(3) at z greater than or similar to 0.5.

      DOI: 10.1103/PhysRevD.80.123503

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    • Nonlinear evolution of the matter power spectrum in modified theories of gravity Peer-reviewed

      Kazuya Koyama, Atsushi Taruya, Takashi Hiramatsu

      Physical Review D - Particles, Fields, Gravitation and Cosmology79 ( 12 )   18 6 2009

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      We present a formalism to calculate the nonlinear matter power spectrum in modified gravity models that explain the late-time acceleration of the Universe without dark energy. Any successful modified gravity models should contain a mechanism to recover general relativity (GR) on small scales in order to avoid the stringent constrains on deviations from GR at solar system scales. Based on our formalism, the quasi-nonlinear power spectrum in the Dvali-Gabadadze- Porratti braneworld models and f(R) gravity models are derived by taking into account the mechanism to recover GR properly. We also extrapolate our predictions to fully nonlinear scales using the parametrized post-Friedmann framework. In the Dvali-Gabadadze-Porratti and f(R) gravity models, the predicted nonlinear power spectrum is shown to reproduce N-body results. We find that the mechanism to recover GR suppresses the difference between the modified gravity models and dark energy models with the same expansion history, but the difference remains large at the weakly nonlinear regime in these models. Our formalism is applicable to a wide variety of modified gravity models and it is ready to use once consistent models for modified gravity are developed. © 2009 The American Physical Society.

      DOI: 10.1103/PhysRevD.79.123512

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    • Nonlinear evolution of the matter power spectrum in modified theories of gravity Peer-reviewed

      Kazuya Koyama, Atsushi Taruya, Takashi Hiramatsu

      PHYSICAL REVIEW D79 ( 12 )   6 2009

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      We present a formalism to calculate the nonlinear matter power spectrum in modified gravity models that explain the late-time acceleration of the Universe without dark energy. Any successful modified gravity models should contain a mechanism to recover general relativity (GR) on small scales in order to avoid the stringent constrains on deviations from GR at solar system scales. Based on our formalism, the quasi-nonlinear power spectrum in the Dvali-Gabadadze-Porratti braneworld models and f(R) gravity models are derived by taking into account the mechanism to recover GR properly. We also extrapolate our predictions to fully nonlinear scales using the parametrized post-Friedmann framework. In the Dvali-Gabadadze-Porratti and f(R) gravity models, the predicted nonlinear power spectrum is shown to reproduce N-body results. We find that the mechanism to recover GR suppresses the difference between the modified gravity models and dark energy models with the same expansion history, but the difference remains large at the weakly nonlinear regime in these models. Our formalism is applicable to a wide variety of modified gravity models and it is ready to use once consistent models for modified gravity are developed.

      DOI: 10.1103/PhysRevD.79.123512

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    • Chasing the nonlinear evolution of matter power spectrum with a numerical resummation method: Solution of closure equations Peer-reviewed

      Takashi Hiramatsu, Atsushi Taruya

      PHYSICAL REVIEW D79 ( 10 )   5 2009

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      We present a new numerical scheme to treat the nonlinear evolution of cosmological power spectra. Governing equations for matter power spectra have been previously derived by a nonperturbative technique with closure approximation. Solutions of the resultant closure equations just correspond to the resummation of an infinite class of perturbation corrections, and they consistently reproduce the one-loop results of standard perturbation theory. We develop a numerical algorithm to solve closure evolutions in both perturbative and nonperturbative regimes. The present numerical scheme is particularly suited for examining nonlinear matter power spectrum in general cosmological models, including modified theory of gravity. As a demonstration, we study weakly nonlinear evolution of power spectrum in a class of modified gravity models, as well as various dark energy models.

      DOI: 10.1103/PhysRevD.79.103526

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    • Chasing the nonlinear evolution of matter power spectrum with a numerical resummation method: Solution of closure equations Peer-reviewed

      Takashi Hiramatsu, Atsushi Taruya

      Physical Review D - Particles, Fields, Gravitation and Cosmology79 ( 10 )   1 5 2009

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      We present a new numerical scheme to treat the nonlinear evolution of cosmological power spectra. Governing equations for matter power spectra have been previously derived by a nonperturbative technique with closure approximation. Solutions of the resultant closure equations just correspond to the resummation of an infinite class of perturbation corrections, and they consistently reproduce the one-loop results of standard perturbation theory. We develop a numerical algorithm to solve closure evolutions in both perturbative and nonperturbative regimes. The present numerical scheme is particularly suited for examining nonlinear matter power spectrum in general cosmological models, including modified theory of gravity. As a demonstration, we study weakly nonlinear evolution of power spectrum in a class of modified gravity models, as well as various dark energy models. © 2009 The American Physical Society.

      DOI: 10.1103/PhysRevD.79.103526

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    • DECIGO pathfinder Peer-reviewed

      Masaki Ando, Seiji Kawamura, Shuichi Sato, Takashi Nakamura, Kimio Tsubono, Akito Araya, Ikkoh Funaki, Kunihito Ioka, Nobuyuki Kanda, Shigenori Moriwaki, Mitsuru Musha, Kazuhiro Nakazawa, Kenji Numata, Shin-ichiro Sakai, Naoki Seto, Takeshi Takashima, Takahiro Tanaka, Kazuhiro Agatsuma, Koh-suke Aoyanagi, Koji Arai, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Yumiko Ejiri, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Katsuhiko Ganzu, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Nobuki Kawashima, Fumiko Kawazoe, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hideaki Kudoh, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei-ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Shinji Miyoki, Mutsuko Y. Morimoto, Tomoko Morioka, Toshiyuki Morisawa, Shinji Mukohyama, Shigeo Nagano, Isao Naito, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Taiga Noumi, Yoshiyuki Obuchi, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Norio Okada, Kouji Onozato, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Masaaki Sakagami, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Rieko Suzuki, Hideyuki Tagoshi, Fuminobu Takahashi, Kakeru Takahashi, Keitaro Takahashi, Ryutaro Takahashi, Ryuichi Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Takamori Akiteru, Tadashi Takano, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Yasuo Torii, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Akitoshi Ueda, Ken-ichi Ueda, Masayoshi Utashima, Yaka Wakabayashi, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Jun'ichi Yokoyama, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino

      CLASSICAL AND QUANTUM GRAVITY26 ( 9 )   5 2009

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      DECIGO pathfinder (DPF) is a milestone satellite mission for DECIGO (DECi-hertz Interferometer Gravitational wave Observatory), which is a future space gravitational wave antenna. DECIGO is expected to provide fruitful insights into the universe, particularly about dark energy, the formation mechanism of supermassive black holes and the inflation of the universe. Since DECIGO will be an extremely challenging mission, which will be formed by three drag-free spacecraft with 1000 km separation, it is important to increase the technical feasibility of DECIGO before its planned launch in 2024. Thus, we are planning to launch two milestone missions: DPF and pre-DECIGO. In this paper, we review the conceptual design and current status of the first milestone mission, DPF.

      DOI: 10.1088/0264-9381/26/9/094019

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    • A closure theory for nonlinear evolution of cosmological power spectra Peer-reviewed

      Katsushi Taruya, Takashi Hiramatsu

      Astrophysical Journal674 ( 2 ) 617 - 635   20 2 2008

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:Institute of Physics Publishing  

      We apply a nonlinear statistical method in turbulence to the cosmological perturbation theory and derive a closed set of evolution equations for matter power spectra. The resultant closure equations consistently recover the one-loop results of standard perturbation theory, and beyond that, it is still capable of treating the nonlinear evolution of matter power spectra. We find the exact integral expressions for the solutions of closure equations. These analytic expressions coincide with the renormalized one-loop results presented by Crocce and Scoccimarro apart from the vertex renormalization. By constructing the nonlinear propagator, we analytically evaluate the nonlinear matter power spectra based on the first-order Born approximation of the integral expressions and compare it with those of the renormalized perturbation theory. © 2008. The American Astronomical Society. All rights reserved.

      DOI: 10.1086/526515

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    • High-energy effects on the spectra of cosmological perturbations in braneworld cosmology Peer-reviewed

      T. Hiramatsu, K. Koyama, A. Taruya

      11th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proc. of the MG11 Meeting on General Relativity   2824 - 2826   2008

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    • Scalar perturbations in braneworld cosmology Peer-reviewed

      Antonio Cardoso, Takashi Hiramatsu, Kazuya Koyama, Sanjeev S. Seahra

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 7 )   7 2007

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      We study the behaviour of scalar perturbations in the radiation-dominated era of Randall-Sundrum braneworld cosmology by numerically solving the coupled bulk and brane master wave equations. We find that density perturbations with wavelengths less than a critical value ( set by the bulk curvature length) are amplified during horizon re-entry. This means that the radiation-era matter power spectrum will be at least an order of magnitude larger than the predictions of general relativity (GR) on small scales. Conversely, we explicitly confirm from simulations that the spectrum is identical to GR on large scales. Although this magnification is not relevant for the cosmic microwave background or measurements of large scale structure, it will have some bearing on the formation of primordial black holes in Randall-Sundrum models.

      DOI: 10.1088/1475-7516/2007/07/008

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    • Primordial perturbations from slow-roll inflation on a brane Peer-reviewed

      Kazuya Koyama, Andrew Mennim, V. A. Rubakov, David Wands, Takashi Hiramatsu

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 4 )   4 2007

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      In this paper we quantize scalar perturbations in a Randall Sundrum- type model of inflation where the inflaton field is confined to a single brane embedded in five-dimensional anti-de Sitter space-time. In the high energy regime, small-scale in inflaton fluctuations are strongly coupled to metric perturbations in the bulk and gravitational back-reaction has a dramatic effect on the behaviour of inflaton perturbations on sub-horizon scales. This is in contrast to the standard four-dimensional result where gravitational back-reaction can be neglected on small scales. Nevertheless, this does not give rise to signifacant particle production, and the correction to the power spectrum of the curvature perturbations on super-horizon scales is shown to be suppressed by a slow-roll parameter. We calculate the complete first-order slow-roll corrections to the spectrum of primordial curvature perturbations.

      DOI: 10.1088/1475-7516/2007/04/001

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    • Detecting a stochastic background of gravitational waves in the presence of non-Gaussian noise: A performance of generalized cross-correlation statistic Peer-reviewed

      Yoshiaki Himemoto, Atsushi Taruya, Hideaki Kudoh, Takashi Hiramatsu

      PHYSICAL REVIEW D75 ( 2 )   1 2007

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

      We discuss a robust data analysis method to detect a stochastic background of gravitational waves in the presence of non-Gaussian noise. In contrast to the standard cross-correlation (SCC) statistic frequently used in the stochastic background searches, we consider a generalized cross-correlation (GCC) statistic, which is nearly optimal even in the presence of non-Gaussian noise. The detection efficiency of the GCC statistic is investigated analytically, particularly focusing on the statistical relation between the false-alarm and the false-dismissal probabilities, and the minimum detectable amplitude of gravitational-wave signals. We derive simple analytic formulas for these statistical quantities. The robustness of the GCC statistic is clarified based on these formulas, and one finds that the detection efficiency of the GCC statistic roughly corresponds to the one of the SCC statistic neglecting the contribution of non-Gaussian tails. This remarkable property is checked by performing the Monte Carlo simulations and successful agreement between analytic and simulation results was found.

      DOI: 10.1103/PhysRevD.75.022003

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    • Numerical study of curvature perturbations in a brane-world inflation at high-energies Peer-reviewed

      Takashi Hiramatsu, Kazuya Koyama

      JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS ( 12 )   12 2006

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      We study the evolution of scalar curvature perturbations in a brane-world inflation model in a 5D anti-de Sitter space-time. The inflaton perturbations are confined to a 4D brane but they are coupled to the 5D bulk metric perturbations. We numerically solve full coupled equations for the inflaton perturbations and the 5D metric perturbations using the Hawkins-Lidsey inflationary model. At an initial time, we assume that the bulk is unperturbed. We find that the inflaton perturbations at high energies are strongly coupled to the bulk metric perturbations even on subhorizon scales, leading to the suppression of the amplitude of the comoving curvature perturbations at a horizon crossing. This indicates that the linear perturbations of the inflaton field do not obey the usual 4D Klein-Gordon equation due to the coupling to 5D gravitational fields on small scales, and it is necessary to quantize the coupled brane-bulk system in a consistent way in order to calculate the spectrum of the scalar perturbations in a brane-world inflation.

      DOI: 10.1088/1475-7516/2006/12/009

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    • High-energy effects on the spectrum of the inflationary gravitational wave background in braneworld cosmology Peer-reviewed

      T Hiramatsu

      PHYSICAL REVIEW D73 ( 8 )   4 2006

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      We discuss the cosmological evolution of the inflationary gravitational wave background in the Randall-Sundrum single-brane model. In braneworld cosmology, in which the three-dimensional spacelike hypersurface that we live in is embedded in five-dimensional anti-de-Sitter (AdS(5)) spacetime, the evolution of gravitational wave (GW) modes is affected by the nonstandard expansion of the universe and the excitation of the Kaluza-Klein modes. These are significant in the high-energy regime of the universe. We numerically evaluate these two effects by solving the evolution equation for GWs propagating through the AdS(5) spacetime. Using a plausible initial condition from inflation, we find that the excitation of Kaluza-Klein modes can be characterized by a simple scaling relation above the critical frequency f(crit) determined from the length scale of the fifth dimension l. The remarkable point is that this relation generally holds as long as the matter content of the universe is described by the perfect fluid with the equation of state p=w rho for 0 &lt;= w &lt;= 1. The resultant scaling relation is translated into the energy spectrum of the inflationary gravitational wave background as Omega(GW)proportional to f((3w-1)/(3w+2)) for f &gt; f(crit). This indicates that in the radiation dominant case (w=1/3), the two high-energy effects accidentally compensate each other and the spectrum becomes almost the same as the one predicted in the four-dimensional theory, i.e., Omega(GW)proportional to f(0).

      DOI: 10.1103/PhysRevD.73.084008

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    • Detecting a gravitational-wave background with next-generation space interferometers Peer-reviewed

      H Kudoh, A Taruya, T Hiramatsu, Y Himemoto

      PHYSICAL REVIEW D73 ( 6 )   3 2006

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      Future missions of gravitational-wave astronomy will be operated by space-based interferometers, covering a very wide range of frequencies. Search for stochastic gravitational-wave backgrounds (GWBs) is one of the main targets for such missions, and we here discuss the prospects for direct measurement of isotropic and anisotropic components of (primordial) GWBs around the frequency 0.1-10 Hz. After extending the theoretical basis for correlation analysis, we evaluate the sensitivity and the signal-to-noise ratio for the proposed future space interferometer missions, like Big-Bang Observer (BBO), Deci-Hertz Interferometer Gravitational-wave Observer (DECIGO), and the recently proposed Fabry-Perot type DECIGO. The astrophysical foregrounds which are expected at low frequency may be a big obstacle and may significantly reduce the signal-to-noise ratio of GWBs. As a result, the minimum detectable amplitude may reach h(2)Omega(gw) = 10(-15)similar to 10(-16), as long as foreground point sources are properly subtracted. Based on correlation analysis, we also discuss measurement of anisotropies of GWBs. As an example, the sensitivity level required for detecting the dipole moment of GWB induced by the proper motion of our local system is closely examined.

      DOI: 10.1103/PhysRevD.73.064006

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    • Detecting a gravitational-wave background with next-generation space interferometers Peer-reviewed

      Hideaki Kudoh, Atsushi Taruya, Takashi Hiramatsu, Yoshiaki Himemoto

      Physical Review D - Particles, Fields, Gravitation and Cosmology73 ( 6 )   2006

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      Future missions of gravitational-wave astronomy will be operated by space-based interferometers, covering a very wide range of frequencies. Search for stochastic gravitational-wave backgrounds (GWBs) is one of the main targets for such missions, and we here discuss the prospects for direct measurement of isotropic and anisotropic components of (primordial) GWBs around the frequency 0.1-10 Hz. After extending the theoretical basis for correlation analysis, we evaluate the sensitivity and the signal-to-noise ratio for the proposed future space interferometer missions, like Big-Bang Observer (BBO), Deci-Hertz Interferometer Gravitational-wave Observer (DECIGO), and the recently proposed Fabry-Perot type DECIGO. The astrophysical foregrounds which are expected at low frequency may be a big obstacle and may significantly reduce the signal-to-noise ratio of GWBs. As a result, the minimum detectable amplitude may reach h2Ωgw=10-15∼10-16, as long as foreground point sources are properly subtracted. Based on correlation analysis, we also discuss measurement of anisotropies of GWBs. As an example, the sensitivity level required for detecting the dipole moment of GWB induced by the proper motion of our local system is closely examined. © 2006 The American Physical Society.

      DOI: 10.1103/PhysRevD.73.064006

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    • Detecting a stochastic background of gravitational waves in the presence of non-Gaussian noise Peer-reviewed

      Y. Himemoto, A. Taruya, H. Kudoh, T. Hiramatsu

      LASER INTERFEROMETER SPACE ANTENNA873   471 - +   2006

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      Language:English   Publishing type:Research paper (international conference proceedings)   Publisher:AMER INST PHYSICS  

      We discuss the robust data analysis method to detect a stochastic background of gravitational waves in the presence of non-Gaussian noise. Usually, the so-called standard cross-correlation (SCC) statistic is used for the data analysis of gravitational-wave background search, which is optimal only if the detector noise obeys a stationary Gaussian process. Here, we consider a generalized cross-correlation (GCC) statistic, which is nearly optimal even in the presence of non-Gaussian noise. The detection efficiency and the general tendency of the GCC statistic are investigated analytically, particularly focusing on the statistical quantities of the false-alarm and the false-dismissal probabilities and the minimum detectable amplitude of gravitational-wave signals. We find that the GCC statistics is robust against the non-Gaussian tail of detector noises.

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    • Gravitational wave background from neutrino-driven gamma-ray bursts Peer-reviewed

      T Hiramatsu, K Kotake, H Kudoh, A Taruya

      MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY364 ( 3 ) 1063 - 1068   12 2005

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:BLACKWELL PUBLISHING  

      We discuss the gravitational wave background (GWB) from a cosmological population of gamma-ray bursts (GRBs). Among the various emission mechanisms for the gravitational waves (GWs), we pay particular attention to the vast anisotropic neutrino emissions from the accretion discs around black holes formed after so-called failed supernova explosions. The GWs produced by such mechanisms are known as 'burst with memory', and could dominate in the low-frequency regime below similar to 10 Hz. To estimate their amplitudes, we derive general analytic formulae for gravitational waveforms from the axisymmetric jets. Based on the formulae, we first quantify the spectrum of GWs from a single GRB. Then, summing the cosmological population, we find that the resultant value of the density parameter becomes roughly Omega(GW) approximate to 10(-20) over the wide-band of the low-frequency region, f similar to 10(-4) Hz. The amplitude of the GWB is significantly smaller than that of the primordial GWB originating from the inflationary epoch, and is far below the detection limit.

      DOI: 10.1111/j.1365-2966.2005.09643.x

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    • Evolution of gravitational waves in the high-energy regime of brane-world cosmology Peer-reviewed

      T Hiramatsu, K Koyama, A Taruya

      PHYSICS LETTERS B609 ( 1-2 ) 133 - 142   3 2005

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

      We discuss the evolution of gravitational waves (GWs) after inflation in a brane-world cosmology embedded in five-dimensional anti-de Sitter (AdS(5)) bulk spacetime. In a brane-world scenario, the evolution of GWs is affected by the nonstandard cosmological expansion and the excitation of the Kaluza-Klein (KK) modes, which are significant in the high-energy regime of the universe. We numerically solve the wave equation of GWs in the Poincare coordinates of the AdS5 spacetime. Using a plausible initial condition from inflation, we find that, while the behavior of GWs in the bulk is sensitive to the transition time from inflation to the radiation-dominated epoch, the amplitude of GWs on the brane is insensitive to this time if the transition occurs early enough before horizon reentry. As a result, the amplitude of GWs is suppressed by the excitation of KK-modes and the effect may compensate the enhancement of the GWs by the non-standard cosmological expansion. Based on this, the influence of the high-energy effects on the GW backgrounds is discussed. (C) 2005 Elsevier B.V. All rights reserved.

      DOI: 10.1016/j.physletb.2005.01.024

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    • Evolution of gravitational waves from inflationary brane-world: numerical study of high-energy effects Peer-reviewed

      T Hiramatsu, K Koyama, A Taruya

      PHYSICS LETTERS B578 ( 3-4 ) 269 - 275   1 2004

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

      We study the evolution of gravitational waves (GWs) after inflation in a brane-world cosmology embedded in five-dimensional anti-de Sitter space-time. Contrary to the standard four-dimensional results, the GWs at the high-energy regime in brane-world model suffer from the effects of the non-standard cosmological expansion and the excitation of the Kaluza-Klein modes (KK-modes), which can affect the amplitude of stochastic gravitational wave background significantly. To investigate these two high-energy effects quantitatively, we numerically solve the wave equation of the GWs in the radiation dominated epoch at relatively low-energy scales. We show that the resultant GWs are suppressed by the excitation of the KK modes. The created KK modes are rather soft and escape away from the brane to the bulk gravitational field. The results are also compared to the semi-analytic prediction from the low-energy approximation and the evolved amplitude of GWs on the brane reasonably matches the numerical simulations. (C) 2003 Published by Elsevier B.V.

      DOI: 10.1016/j.physletb.2003.10.111

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    Misc.

    • Gravitational waves from cosmic string - domain wall networks

      Takashi Hiramatsu, Masahiro Kawasaki, Ken’ichi Saikawa, Toyokazu Sekiguchi

      Proceedings in the 21st workshop on General Relativity and Gravitation in Japan (JGRG21)   2012

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    • Preface Peer-reviewed

      T. Hiramatsu, M. Sasaki, M. Shibata, T. Shiromizu

      Proceedings of the 20th Workshop on General Relativity and Gravitation in Japan, JGRG 2010   xv   2010

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    • DECIGO: The Japanese space gravitational wave antenna Peer-reviewed

      Shuichi Sato, Seiji Kawamura, Masaki Ando, Takashi Nakamura, Kimio Tsubono, Akito Araya, Ikkoh Funaki, Kunihito Ioka, Nobuyuki Kanda, Shigenori Moriwaki, Mitsuru Musha, Kazuhiro Nakazawa, Kenji Numata, Shin Ichiro Sakai, Naoki Seto, Takeshi Takashima, Takahiro Tanaka, Kazuhiro Agatsuma, Koh Suke Aoyanagi, Koji Arai, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Yumiko Ejiri, Motohiro Enoki, Yoshiharu Eriguchi, Masa Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Katsuhiko Ganzu, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki TInoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Nobuki Kawashima, Fumiko Kawazoe, Kishimoto Naoko, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hideaki Kudoh, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei Ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Shinji Miyoki, Mutsuko YMorimoto, Tomoko Morioka, Toshiyuki Morisawa, Shinji Mukohyama, Shigeo Nagano, Isao Naito, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Taiga Noumi, Yoshiyuki Obuchi, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Norio Okada, Kouji Onozato, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Masaaki Sakagami, Shihori Sakata, Misao Sasaki

      Journal of Physics: Conference Series154   2009

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      DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the planned Japanese space gravitational wave antenna, aiming to detect gravitational waves from astrophysically and cosmologically significant sources mainly between 0.1 Hz and 10 Hz and thus to open a new window for gravitational wave astronomy and for the universe. DECIGO will consist of three drag-free spacecraft, 1000 km apart from each other, whose relative displacements are measured by a differential Fabry-Perot interferometer. We plan to launch DECIGO in middle of 2020s, after sequence of two precursor satellite missions, DECIGO pathfinder and Pre-DECIGO, for technology demonstration required to realize DECIGO and hopefully for detection of gravitational waves from our galaxy or nearby galaxies. © 2009 IOP Publishing Ltd.

      DOI: 10.1088/1742-6596/154/1/012040

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    • The Japanese Space Gravitational Wave Antenna; DECIGO Peer-reviewed

      Seiji Kawamura, Masaki Ando, Takashi Nakamura, Kimio Tsubono, Takahiro Tanaka, Ikkoh Funaki, Naoki Seto, Kenji Numata, Shuichi Sato, Kunihito Ioka, Nobuyuki Kanda, Takeshi Takashima, Kazuhiro Agatsuma, Tomotada Akutsu, Tomomi Akutsu, Koh-suke Aoyanagi, Koji Arai, Yuta Arase, Akito Araya, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Katsuhiko Ganzu, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Shogo Kamagasako, Nobuki Kawashima, Fumiko Kawazoe, Hiroyuki Kirihara, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hideaki Kudoh, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei-ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Shinji Miyoki, Mutsuko Y. Morimoto, Tomoko Morioka, Toshiyuki Morisawa, Shigenori Moriwaki, Shinji Mukohyama, Mitsuru Musha, Shigeo Nagano, Isao Naito, Noriyasu Nakagawa, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Akira Okutomi, Kouji Onozato, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Masaaki Sakagami, Shin-ichiro Sakai, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Hideyuki Tagoshi, Kakeru Takahashi, Keitaro Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Ryuichi Takahashi, Ryutaro Takahashi, Akiteru Takamori, Tadashi Takano, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Mitsuru Tokuda, Masao Tokunari, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Ken-ichi Ueda, Masayoshi Utashima, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Jun'ichi Yokoyama, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino

      TAUP2007: TENTH INTERNATIONAL CONFERENCE ON TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS120   2008

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      Language:English   Publisher:IOP PUBLISHING LTD  

      DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the future Japanese space gravitational wave antenna. DECIGO is expected to open a new window of observation for gravitational wave astronomy especially between 0.1 Hz and 10 Hz, revealing various mysteries of the universe such as dark energy, formation mechanism of supermassive black holes, and inflation of the universe. The pre-conceptual design of DECIGO consists of three drag-free spacecraft, whose relative displacements are measured by a differential Fabry-Perot Michelson interferometer. We plan to launch two missions, DECIGO pathfinder and pre-DECIGO first and finally DECIGO in 2024.

      DOI: 10.1088/1742-6596/120/3/032004

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    Presentations

    • Testing gravity with CMB

      Takashi Hiramatsu

      JGRG29  25 11 2019 

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    • Testing gravity with CMB

      Takashi Hiramatsu

      Theoretical aspects of non-Gaussianity from modern perspectives  18 11 2019 

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    • Cosmological gravitational wave background and very early Universe Invited

      Takashi Hiramatsu

      ICRR public lecture  26 10 2019 

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      Language:Japanese   Presentation type:Public lecture, seminar, tutorial, course, or other speech  

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    • Testing gravity with CMB

      Takashi Hiramatsu

      Autumn meeting of Physics Society in Japan  17 9 2019 

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    • Oscillons after inflation and gravitational waves International conference

      Takashi Hiramatsu

      COSMO-19  2 9 2019 

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    • Parasitic higher winding strings in Abelian-Higgs model

      Takashi Hiramatsu

      Planet2 / RESCEU Summer School, From the Solar System to the Universe  23 8 2019 

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    • Oscillons after inflation and gravitational waves

      Takashi Hiramatsu

      Resonant instabilities in cosmology and their observational consequences  7 5 2019 

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    • Oscillons after inflation and gravitational waves

      Takashi Hiramatsu

      74th Annual Meeting of The Physical Society of Japan  14 3 2019 

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    • Hunting for Statistical Anisotropy in Tensor Modes with B-mode Observations International conference

      Takashi Hiramatsu

      Accelerating Universe in the Dark  5 3 2019 

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    • Hunting for Statistical Anisotropy in Tensor Modes with B-mode Observations International conference

      Takashi Hiramatsu

      2019 YITP Asian-Pacific Winter School and Workshop on Gravitation and Cosmology  11 2 2019 

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    • Hunting for Statistical Anisotropy in Tensor Modes with B-mode observations

      Takashi Hiramatsu

      Workshop on observational cosmology  12 11 2018 

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      Venue:Yamaguchi University  

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    • CMB Bispectra induced by lensing

      Takashi Hiramatsu

      28th JGRG  5 11 2018 

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      Venue:Rikkyo University  

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    • Statistical anisotropy of CMB B-mode

      Takashi Hiramatsu

      JPS autumn meeting  14 9 2018 

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      Venue:Shinshu University  

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    • Gravitational waves from cosmic string networks International conference

      Takashi Hiramatsu

      15th Mercel Grossmann Meeting  1 7 2018 

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      Venue:Roma University  

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    • Dynamical screening of scalar waves in Cubic Galileon model International conference

      Takashi Hiramatsu

      Workshop “Essential next steps for gravity and cosmology”  18 5 2018 

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      Venue:Tohoku Univ.  

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    • Computing CMB bispectra

      Takashi Hiramatsu

      Bispectrum workshop  29 3 2018 

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      Venue:Kyoto University  

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    • Reconstruction of primordial tensor power spectrum from B-mode observations

      Takashi Hiramatsu

      Yamaguchi workshop  13 3 2018 

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      Venue:Yamaguchi University  

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    • Dynamical screening of scalar waves in Cubic Galileon model International conference

      Takashi Hiramatsu

      GC2018  2 3 2018 

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      Venue:Kyoto University  

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    • Reconstruction of primordial tensor power spectrum from B-mode observations International conference

      Takashi Hiramatsu

      YKIS2018 “General Relativity ? The Next Generation ?“  19 2 2018 

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      Venue:Kyoto University  

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    • Reconstruction of primordial tensor power spectrum from B-mode observations International conference

      Takashi Hiramatsu

      Symposium “Why does the Universe accelerate ?”  10 2 2018 

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      Venue:Tohoku Univ.  

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    • Field-theoretic simulations of colliding superconducting strings International conference

      Takashi Hiramatsu

      CosPA 2017  11 12 2017 

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      Venue:Kyoto University  

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    • Reconstruction of primordial tensor power spectrum from B-mode observations International conference

      Takashi Hiramatsu

      27th JGRG  27 11 2017 

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      Venue:Hiroshima University  

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    • Reconstruction of primordial tensor power spectrum from B-mode observations International conference

      Takashi Hiramatsu

      Joint meeting of A01,A03,B01 groups in Innovative Areas “Why does the Universe accelerate?”  25 9 2017 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:Nagoya University  

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    • Reconstruction of primordial tensor power spectrum from B-mode observations

      Takashi Hiramatsu

      JPS autumn meeting  12 9 2017 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Utsunomiya University  

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    • Gravitational clustering of massive neutrinos around cold dark matter halos International conference

      Takashi Hiramatsu

      ICG-NAOC-YITP joint workshop “Next-generation cosmology with large-scale structure”  4 9 2017 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:Kyoto University  

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    • Field-theoretic simulations of colliding superconducting strings International conference

      Takashi Hiramatsu

      COSMO-17  28 8 2017 

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      Venue:UPMC, Paris  

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    • Vainshtein mechanism fro non-spherical matter distribution in Cubic Galileon model

      Takashi Hiramatsu

      Tohoku workshop  9 8 2017 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Tohoku University  

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    • Reconstruction of primordial tensor power spectrum from B-mode observations International conference

      Takashi Hiramatsu

      RESCEU summer school  29 7 2017 

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      Venue:Yamaguchi University  

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    • Gravitational waves from cosmic strings

      Takashi Hiramatsu

      72th JPS annual meeting  17 3 2017 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Osaka University  

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    • A new code for non-linear evolution of CMB anisotropy International conference

      Takashi Hiramatsu

      Symposium “Why does the Universe accelerate ?”  8 3 2017 

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      Venue:KEK  

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    • Colliding strings coupled to matter field International conference

      Takashi Hiramatsu

      26th JGRG  24 10 2016 

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      Venue:Osaka City Univ.  

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    • CMB bispectrum of tensor perturbations

      Takashi Hiramatsu

      JPS autumn meeting  21 9 2016 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Miyazaki Univ.  

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    • CMB bispectrum

      Takashi Hiramatsu

      Hirosaki workshop on gravity and cosmology  3 8 2016 

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      Venue:Hirosaki Univ.  

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    • Cosmic strings coupled with scalar matter field

      Takashi Hiramatsu

      71th JPS annual meeting  19 3 2016 

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      Venue:/Tohoku/Univ.  

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    • Cosmic strings and gravitational waves Invited

      Takashi Hiramatsu

      14th DECIGO meeting  18 10 2015 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:TAP, Kyoto Univ.  

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    • CMB bispectrum International conference

      Takashi Hiramatsu

      COSMO-15  7 9 2015 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:Uniwersytet Warszawski  

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    • CMB bispectrum International conference

      Takashi Hiramatsu

      RESCEU/APCosPa Summer School on Cosmology and Particle Astrophysics  1 8 2015 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:Kinugawa  

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    • The CMB bispectrum from nonlinear evolution after inflation : numerical code

      Takashi Hiramatsu

      JPS Autumn Meeting  21 3 2015 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Waseda Univ.  

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    • progress of code development : 2nd-order Einstein-Boltzmann solver for CMB anisotropy

      Takashi Hiramatsu

      3rd Observational Cosmology Workshop  26 11 2014 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Nagoya University  

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    • progress of code development : 2nd-order Einstein-Boltzmann solver for CMB anisotropy International conference

      Takashi Hiramatsu

      24th JGRG  10 11 2014 

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      Venue:Kavli IPMU  

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    • progress of code development : 2nd-order Einstein-Boltzmann solver for CMB anisotropy

      Takashi Hiramatsu

      JPS Autumn Meeting  18 9 2014 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Saga University  

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    • progress of code development : 2nd-order Einstein-Boltzmann solver for CMB anisotropy International conference

      Takashi Hiramatsu

      Relativistic Cosmology  8 9 2014 

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      Venue:YITP  

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    • progress of code development : 2nd-order Einstein-Boltzmann solver for CMB anisotropy International conference

      Takashi Hiramatsu

      RESCEU APCosPA Summer School on Cosmology and Particle Astrophysics  31 7 2014 

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      Language:English   Presentation type:Poster presentation  

      Venue:Jimoto-ya  

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    • Bound states of Type-I cosmic strings

      Takashi Hiramatsu

      69th JPS Annual Meeting  27 3 2014 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Tokai University  

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    • Bound states of extreme Type-I cosmic strings in two-dimensional space Invited International conference

      Takashi Hiramatsu

      23th JGRG  5 11 2013 

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      Venue:Hirosaki University  

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    • Instability of colliding metastable strings

      Takashi Hiramatsu

      JPS Autumn Meeting  20 9 2013 

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      Venue:Kouchi University  

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    • Type-I cosmic string network -- network density --

      Takashi Hiramatsu

      JPS Annual Meeting  26 3 2013 

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      Venue:Hiroshima University  

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    • Type-I cosmic string network International conference

      Takashi Hiramatsu

      Nishinomiya Yukawa Symposium: New Waves in Gravity and Cosmology  4 12 2012 

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      Language:English   Presentation type:Poster presentation  

      Venue:YITP  

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    • Equivalence Principle Violation in Vainshtein Screened Two-Body Systems International conference

      Takashi Hiramatsu

      22th JGRG  12 11 2012 

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      Venue:YITP  

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    • Type-I cosmic string network

      Takashi Hiramatsu

      JPS Autumn Meeting  11 9 2012 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Kyoto Sangyo University  

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    • On the Vainshtein mechanism for two body system in DGP model International conference

      Takashi Hiramatsu

      13th Marcel Grossman Meeting  1 7 2012 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:Stockholm University  

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    • On the Vainshtein mechanism for two body system in DGP model

      Takashi Hiramatsu

      JPS autumn meeting  16 9 2011 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Hirosaki University  

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    • On the Vainshtein mechanism for two body system in DGP model International conference

      Takashi Hiramatsu

      COSMO11  22 8 2011 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:da Universidade do Porto  

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    • A head-on approarch for structure formation International conference

      Takashi Hiramatsu

      11th Evolution of spacetime, matter and structure in the Unvierse  25 7 2011 

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      Language:English   Presentation type:Poster presentation  

      Venue:San-ai Kougen Hotel  

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    • Cosmological Lattice Simulations

      Takashi Hiramatsu

      /Next/Astrophysics/Cosmology  24 2 2011 

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      Language:Japanese   Presentation type:Oral presentation (general)  

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    • Gravitational waves from Q-balls in gravity mediation International conference

      Takashi Hiramatsu

      COSMO/CosPA2010  27 9 2010 

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      Venue:University of Tokyo  

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    • Gravitational waves from Q-balls in gravity mediation International conference

      Takashi Hiramatsu

      JGRG20  21 9 2010 

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      Venue:Kyoto University  

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    • Gravitational waves from Q-balls

      Takashi Hiramatsu

      JPS autumn meeting  11 9 2010 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Kyushu Institute of Technology  

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    • Numerical study of Q-ball formation in gravity mediation International conference

      Takashi Hiramatsu

      Summer Institute 2010  4 8 2010 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:Fuji Calm  

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    • Numerical study of Q-ball formation in gravity mediation International conference

      Takashi Hiramatsu

      YKIS symposium 'Cosmology --The next generation --'  28 6 2010 

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      Venue:Yukawa Institute for Theoretical Physics  

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    • Numerical studies on some non-linear phenomena in the early universe International conference

      Takashi Hiramatsu

      Non-gaussianity  24 3 2010 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:Yukawa Institute for Theoretical Physics  

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    • Q-ball charge distribution in the Affleck-Dine mechanism

      Takashi Hiramatsu

      65th JPS annual meeting  20 3 2010 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Okayama University  

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    • Non-linear evolution of matter power spectrum in a closure theory International conference

      Takashi Hiramatsu

      COSMO09  6 9 2009 

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      Language:English   Presentation type:Poster presentation  

      Venue:CERN  

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    • Non-linear evolution of matter power spectrum in a closure theory International conference

      Takashi Hiramatsu

      9th Evolution of spacetime, matter and structure in the Unvierse  30 8 2009 

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    • Non-linear power spectra in closure theory International conference

      Takashi Hiramatsu

      Molecule-workshop "Non-linear cosmological perturbations"  13 4 2009 

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      Venue:Yukawa Institute for Theoretical Physics  

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    • Non-linear power spectra in f(R) gravity and DGP model

      Takashi Hiramatsu

      64th JPS annual meeting  27 3 2009 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Rikkyo University  

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    • Non-linear evolution of matter power spectrum in a closure theory International conference

      Takashi Hiramatsu

      JGRG18  17 11 2008 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:University of Hiroshima  

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    • Non-linear evolution of matter power spectrum in a closure theory International conference

      Takashi Hiramatsu

      RESCEU international symposium  11 11 2008 

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      Language:English   Presentation type:Poster presentation  

      Venue:University of Tokyo  

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    • Non-linear power spectrum in modified gravity theories

      Takashi Hiramatsu

      JPS autumn meeting  20 9 2008 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:University of Yamagata  

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    • 1-loop perturbation theory based on a closure approximation International conference

      Takashi Hiramatsu

      8th Evolution of spacetime, matter and structure in the Unvierse  29 8 2008 

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      Language:English   Presentation type:Poster presentation  

      Venue:Yanagi-no-Yu  

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    • バリオン音響振動の非線形進化・その2

      Takashi Hiramatsu

      63th JPS annual meeting  23 5 2008 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:University of Kinki  

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    • Cosmological power spectra in a closure theory International conference

      Takashi Hiramatsu

      Cosmology Near & Far  19 5 2008 

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      Language:English   Presentation type:Poster presentation  

      Venue:Waikoloa Beach Marriott  

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    • Cosmological perturbations in braneworld International conference

      Takashi Hiramatsu

      17th JGRG  3 12 2007 

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      Venue:University of Nagoya  

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    • Scalar perturbations in braneworld cosmology

      Takashi Hiramatsu

      62th JPS annual meeting  21 9 2007 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:University of Hokkaido  

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    • Scalar perturbations in braneworld cosmology

      Takashi Hiramatsu

      Evolution of spacetime and matter in the early universe  28 5 2007 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:University of Tokyo  

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    • Scalar perturbations in RS single brane model

      Takashi Hiramatsu

      6th RESCEU workshop  18 2 2007 

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      Venue:Hotel Izu-Kougen  

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    • Evolution of curvature perturbations in a brane-world inflation at high-energies International conference

      Takashi Hiramatsu

      Brane workshop  18 9 2006 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:Institute for Cosmology and Gravity  

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    • Evolution of curvature perturbations in a brane-world inflation at high-energies

      Takashi Hiramatsu

      5th RESCEU workshop  3 9 2006 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Kinugawa Onsen Hotel  

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    • /High/effects on the spectra of cosmological perturbations in braneworld cosmology International conference

      Takashi Hiramatsu

      11th Marcel Grossmann Meeting  23 7 2006 

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      Venue:Freie Universtaet Berlin  

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    • Transfer function of tensor perturbations in braneworld cosmology -- brane motion effects --

      Takashi Hiramatsu

      61th JPS annual meeting  27 3 2006 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Matsuyama University  

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    • Numerical study of brane inflaton perturbations

      Takashi Hiramatsu

      JPS autumn meeting  12 9 2005 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:/Osaka/University  

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    • Evolution of gravitational waves in the high-energy regime of brane-world cosmology International conference

      Takashi Hiramatsu

      COSMO05  27 8 2005 

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      Language:English   Presentation type:Oral presentation (general)  

      Venue:University of Bonn  

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    • Numerical study of brane inflaton perturbations

      Takashi Hiramatsu

      RESCEU meeting  22 8 2005 

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      Language:Japanese   Presentation type:Oral presentation (general)  

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    • Evolution of gravitational waves in the high-energy regime of brane-world cosmology International conference

      Takashi Hiramatsu

      YKIS  27 6 2005 

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      Language:English   Presentation type:Poster presentation  

      Venue:Yukawa Institute for Theoretical Physics  

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    • Evolution of gravitational waves in the high-energy regime of brane-world cosmology International conference

      Takashi Hiramatsu

      59th Yamada conference  21 6 2005 

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      Language:English   Presentation type:Poster presentation  

      Venue:University of Tokyo  

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    • Evolution of gravitational waves in the high-energy regime of brane-world cosmology

      Takashi Hiramatsu

      60th JPS annual meeting  26 3 2005 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Tokyo University of Science  

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    • Gravitational wave background from gamma-ray-bursts

      Takashi Hiramatsu

      4th TAMA meeting  16 2 2005 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:/Osaka/University  

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    • Evolution of gravitational waves in the high-energy regime of brane-world cosmology

      Takashi Hiramatsu

      4th TAMA meeting  16 2 2005 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:/Osaka/University  

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    • Evolution of gravitational waves in the high-energy regime of brane-world cosmology

      Takashi Hiramatsu

      14th JGRG  29 11 2004 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Yukawa Institute for Theoretical Physics  

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    • Cosmic gravitational wave background from inflationary braneworld

      Takashi Hiramatsu

      JPS autumn meeting  27 9 2004 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Kochi University  

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    • Evolution of gravitational waves from inflationary braneworld International conference

      Takashi Hiramatsu

      GR17  18 7 2004 

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      Language:English   Presentation type:Poster presentation  

      Venue:Dublin City University  

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    • Evolution of gravitational waves from inflationary brane-world

      Takashi Hiramatsu

      JPS annual meeting  27 3 2004 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Kyuushu University  

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    • Evolution of gravitational waves from inflationary brane-world International conference

      Takashi Hiramatsu

      GW winter school  12 2 2004 

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      Language:English   Presentation type:Poster presentation  

      Venue:Yukawa Institute for Theoretical Physics  

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    • Evolution of gravitational waves from inflationary brane-world

      Takashi Hiramatsu

      13th JGRG  1 12 2003 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:/Osaka/University  

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    • Evolution of gravitational waves from inflationary brane-world

      Takashi Hiramatsu

      6th RESCEU conference  3 11 2003 

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      Language:Japanese   Presentation type:Poster presentation  

      Venue:University of Tokyo  

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    • Numerical study of gravitational wave background in the brane world scenario

      Takashi Hiramatsu

      JPS autumn meeting  14 9 2003 

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      Language:Japanese   Presentation type:Oral presentation (general)  

      Venue:Miyazaki World Convention Center Summit  

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    • Evolution of gravitational waves from inflationary brane-world

      Takashi Hiramatsu

      RESCEU conference  29 8 2003 

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    Teaching Experience

    • 9 2023 - Present 
      Exercises for Basic Mathematics ( Rikkyo University )

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    • 9 2023 - Present 
      Hydrodynamics ( Rikkyo University )

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    • 9 2020 - Present 
      Introductory Astrophysics ( Rikkyo University )

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    • 9 2020 - Present 
      Physics Exercise II ( Rikkyo University )

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    • 4 2020 - Present 
      Introductory Seminar on Basic Physics ( Rikkyo University )

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    • 4 2020 - Present 
      Physics Exrcise III ( Rikkyo University )

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    • 5 2023 - 5 2023 
      Physics Special Lecture C ( Yamagata University )

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    • 9 2020 - 3 2023 
      Mathematics for Physics 3 ( Rikkyo University )

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    • 4 2020 - 8 2022 
      Computer Experiment I ( Rikkyo University )

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    • 4 2017 - 8 2019 
      物理学演習Ⅰ ( 立教大学理学部物理学科 )

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    • 10 2017 - 3 2018 
      宇宙物理特論Ⅰ ( 立教大学理学部物理学科 )

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    Professional Memberships

    Research Projects

    • Search for New Scalar Particles through Gravitational Waves

      Takahiro Tanaka, Sachiko Kuroyanagi, Atsushi Nishizawa, Takashi Hiramatsu

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      4 2023 - 3 2028

      Grant number:23H00110

      Authorship:Coinvestigator(s) 

      Grant amount:\46280000 ( Direct Cost: \35600000 、 Indirect Cost:\10680000 )

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    • 宇宙論的背景重力波による超高エネルギー物理の開拓

      日本学術振興会  科学研究費助成事業 基盤研究(C) 

      平松 尚志

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      4 2021 - 3 2025

      Grant number:21K03559

      Authorship:Principal investigator 

      Grant amount:\3120000 ( Direct Cost: \2400000 、 Indirect Cost:\720000 )

      2021年度は、修正重力理論の一種であり最も広い理論空間を持つ縮退高階微分スカラー・テンソル(DHOST)理論の、ボルツマンソルバーへの実装を完了しました。これを用い、宇宙マイクロ波背景放射(CMB)の観測データに基づく、DHOST 理論の理論パラメータへの制限を行いました。本研究で開発したボルツマンソルバーは、世界で公開されているコードの中で、最も一般的な重力理論を扱えるソルバーとなっています。また、これを応用し、一般相対論を拡張したにも関わらず、一般相対論と同じく2つの自由度しか持たない特殊なスカラー・テンソル理論(2DoF理論)も実装し、そのモデルパラメータへの制限も行いました。それぞれの論文は現在執筆中で、近日中に公開される予定です。
      宇宙論的位相欠陥に関しては、ダークセクターで生成されるモノポールが現実世界での宇宙紐の構造に影響を与え、局所的にはモノポールに見え遠方からは宇宙紐に見える特殊な宇宙紐に関する研究を行いました。単純な大統一理論ではモノポールの大量生成が問題となり、これを回避するためにインフレーション機構が必要となります。しかし、宇宙紐に閉じ込められたモノポールであれば、現実の宇宙に対する影響を抑えることができ、ある程度の存在が許容されます。このため、大統一理論やその有効理論において、理論の許容される範囲が広がる可能性があります。
      また、ここで用いた申請者自身の開発による場の理論的シミュレーションコード自体の開発も進め、京都大学基礎物理学研究所のスーパーコンピュータ Yukawa-21 上での運用を想定し、OpenMP と MPI を用いたハイブリッド並列化を行いました。その結果、Yukawa-21 上でのベンチマークテストで、おおよそ想定した通りの計算時間と精度を達成していることを確認しました。

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    • Surveying the early Universe in numerical cosmology

      Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B) 

      HIRAMATSU Takashi

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      4 2016 - 3 2019

      Grant number:16K17695

      Authorship:Principal investigator 

      Grant amount:\4030000 ( Direct Cost: \3100000 、 Indirect Cost:\930000 )

      In the extremely early Universe, the Universe experienced the extremely high-energy phenomena such as inflation, the reheating process, and the phase transition of vacuum states. In this research, we focused on the high-precision observations of the cosmic microwave background (CMB) and the future observations of the gravitational wave background with space-borne detectors to survey such high-energy phenomena. In particular, we put emphasis on estimating how well we can extract their information from the observations quantitatively using the field-theoretic simulator and the CMB Boltzmann solver that I have been developing. Moreover, we also focused on the generalised theories of gravity beyond the General Relativity (GR) which affect the generation and propagation of gravitational waves, and estimated to what extent we can see the differences from GR.

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    • 宇宙マイクロ波背景放射における揺らぎの非線形進化

      日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型) 

      平松 尚志

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      4 2016 - 3 2018

      Grant number:16H01098

      Authorship:Principal investigator 

      Grant amount:\1950000 ( Direct Cost: \1500000 、 Indirect Cost:\450000 )

      宇宙マイクロ波背景放射(CMB)のBモード偏光揺らぎの大規模観測計画として、日本の LiteBIRD があります。Bモード偏光揺らぎは、インフレーションを初めとする初期宇宙で作られた背景重力波を源泉として生成されるため、その観測によって、初期宇宙起源の背景重力波の存在を裏付けることができます。
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      近年では、インフレーション以外の背景重力波生成機構も提唱されており、Bモード偏光の観測からこれらを峻別する方法が模索されています。本研究では、LiteBIRD を念頭にしたBモード偏光の観測から、背景重力波のスペクトルを再構成することを試みました。LiteBIRD で観測できる波数(~0.04/Mpc)において、背景重力波のスペクトルを有限個のビンに分け、インフレーション起源のスペクトルを基準に各々のビンの高さをパラメータとして Fisher 情報行列を計算し、ビンの高さの観測精度を定量評価しました(arXiv:1803.00176, PRD査読中)。本研究で開発した定式化は、スペクトルをビンで表現し、特定のスペクトルの形を仮定しないのが特徴的で、これによりインフレーション起源のものと、それ以外の様々な生成機構を経て作られる背景重力波とを一括して取り扱うことが可能になりました。また、本研究を基に、任意の背景重力波スペクトルの観測可能性を議論するのに便利なウェブツール SRec を開発し、これを公開しました。
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      本研究の基盤として開発を行ったボルツマン方程式解法ソフトウェアに関しては、スカラー/ベクトル/テンソル型の温度/Eモード/Bモード揺らぎに対する重力レンズ効果(勾配モード/回転モード)によるパワースペクトル/バイスペクトルを、全てのパターンについて計算できるようになりました。これは、これまで知られているこの種のコードの中では最も一般的なものであり、一般への公開を検討しています。

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    • Non-linear evolution of density fluctuations in numerical cosmology

      Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B) 

      HIRAMATSU Takashi

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      2011 - 2013

      Grant number:23740186

      Authorship:Principal investigator 

      Grant amount:\3510000 ( Direct Cost: \2700000 、 Indirect Cost:\810000 )

      As a first step of establishing the foundations of Numerical Cosmology, we developed a general-purpose three-dimensional hyperbolic equation solver for classical field theory, and studied the non-linear evolution of primordial density fluctuations and the topological defects appeared as a result of phase transition of the vacuum states. As for the latter project, we addressed a variety of issues lying across cosmology by virtue of the ubiquitous property of Numerical Cosmology, from the gravitational waves and axions from domain walls, to the dynamical constraints on the model building of supersymmetric models from the colliding meta-stable strings. In addition, we developed a Boltzmann solver for the photons in the early Universe to impose the initial conditions of the density fluctuations. As for the modified gravity theories, we investigated the details of the scalar gravity hidden in the theories, and the possibility of the observational constraints on their theoretical parameters.

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    • 宇宙背景重力波の起源とその検出可能性の理論的研究

      日本学術振興会  科学研究費助成事業 特別研究員奨励費 

      平松 尚志

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      2004 - 2006

      Grant number:04J11374

      Authorship:Principal investigator 

      Grant amount:\2800000 ( Direct Cost: \2800000 )

      Randall-Sundrumモデルにおける背景重力波の進化について、数値計算の手法を用いて解析した。余剰次元が存在すると、重力波は、フリードマン方程式の高エネルギー補正に伴う増幅効果と、Kaluza-Kleinモードの励起による減衰効果を同時に受ける。本研究の解析により、輻射優勢期においては二つの効果が相殺し、余剰次元が存在するにもかかわらず背景重力波のスペクトルが4次元理論で予言されるものとほぼ同じになることが示された。また、宇宙の状態方程式変えて同様の解析を行った結果、Kaluza-Kleinモードの励起に関してある普遍的な法則があることを示した。
      こういった背景重力波の検出(観測)の際には、一般的に非ガウシアン的雑音の存在を考慮する必要がる。本研究では、一般化された背景重力波信号の相関関数を用いることで、背景重力波の検出効率が増加することを示した。
      インフレーション中には、背景重力波(テンソル)と共に曲率揺らぎ(スカラー)も生成される。本研究では、RSモデルにおけるブレーンインフレーションモデルの1つであるHawkins-Lidseyモデルを用いて、インフラトン場の揺らぎと曲率揺らぎの進化について、古典論の範囲での数値シミュレーションを行った。その結果、小スケールの揺らぎほど振幅が抑えられることが分かった。これは、ブレーン上に束縛されているインフラトン場の揺らぎの一部が、それと結合する曲率揺らぎを介して余剰次元方向へと逃げ出すことによる。
      さらに、本研究はインフラトン揺らぎと曲率揺らぎとの結合系を量子論的に取り扱うことに成功し、インフレーション中における曲率揺らぎの振幅を半解析的に求めた。この解析から、時空が5次元的に振る舞うことによる曲率揺らぎのパワースペクトルの補正は、4次元理論におけるStewart-Lyth補正と同程度であることが示された。

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