Updated on 2024/05/23

写真b

 
ISHII Takaaki
 
*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
Campus Career*
  • 9 2021 - Present 
    College of Science   Department of Physics   Assistant Professor
 

Research Areas

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

Research History

  • 10 2018 - 8 2021 
    Kyoto University   Graduate School of Science Division of Physics and Astronomy   Postdoctoral Researcher

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    Country:Japan

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  • 10 2017 - 9 2018 
    Utrecht University   Institute for Theoretical Physics   Research Associate

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    Country:Netherlands

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  • 9 2015 - 9 2017 
    University of Colorado Boulder   Department of Physics   Research Associate

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    Country:United States

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  • 9 2013 - 8 2015 
    University of Crete   Department of Physics   Postdoctoral Researcher

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    Country:Greece

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  • 10 2011 - 8 2013 
    Seoul National University   Department of Physics and Astronomy   Postdoctoral Researcher

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    Country:Korea, Republic of

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  • 4 2011 - 9 2011 
    University of Cambridge   Department of Applied Mathematics and Theoretical Physics   Research Associate

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    Country:United Kingdom

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  • 4 2010 - 3 2011 
    RIKEN   RIKEN Nishina Center for Accelerator-Based Science   JSPS Research Fellow

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    Country:Japan

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  • 4 2009 - 3 2010 
    Osaka University   Graduate School of Science, Department of Physics   JSPS Research Fellow

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    Country:Japan

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Education

  • 4 2005 - 3 2010 
    Osaka University   Graduate School of Science   Department of Physics

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    Country: Japan

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  • 4 2001 - 3 2005 
    Osaka University   School of Science   Department of Physics

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    Country: Japan

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Papers

  • Turbulence on open string worldsheets under non-integrable boundary conditions

    Takaaki Ishii, Ryo Kitaku, Keiju Murata, Chul-Moon Yoo

    Journal of High Energy Physics2024 ( 2 )   21 2 2024

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

    Abstract

    We demonstrate the turbulent dynamics of the Nambu-Goto open string in the AdS<sub>3</sub> spacetime. While the motion of a classical closed string in AdS is known to be integrable, the integrability of an open string motion depends on the boundary conditions at the string endpoints. We numerically solve the equations of motion of the open string under the boundary conditions where the endpoints are i) fixed to a finite radial coordinate in AdS, and ii) free. For i), we find turbulence on the string, that shows a cascade in the energy and angular momentum spectra. This result indicates the non-integrability of the open string with this type of boundary conditions. For ii), we find no turbulence. This is consistent with the integrability of the open string with the free boundary conditions.

    DOI: 10.1007/jhep02(2024)149

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    Other Link: https://link.springer.com/article/10.1007/JHEP02(2024)149/fulltext.html

  • Boundary driven turbulence on string worldsheet

    Takaaki Ishii, Keiju Murata, Kentaroh Yoshida

    Journal of High Energy Physics2024 ( 1 )   15 1 2024

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

    Abstract

    We study the origin of turbulence on the string worldsheet with boundaries laid in anti de Sitter (AdS) spacetime. While the classical motion of a single closed string in AdS is integrable, it has recently been recognized that weak turbulence arises in the case of an open string suspended from the AdS boundary. In the open string case, it is necessary to impose boundary conditions on the worldsheet boundaries. We classify which boundary conditions preserve integrability. Based on this classification, we anticipate that turbulence may occur on the string worldsheet if integrability is not guaranteed by the boundary conditions. Numerical investigations of the classical open-string dynamics support that turbulence occurs when the boundary conditions are not integrable.

    DOI: 10.1007/jhep01(2024)073

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    Other Link: https://link.springer.com/article/10.1007/JHEP01(2024)073/fulltext.html

  • Hairy black holes in AdS with Robin boundary conditions

    Tomohiro Harada, Takaaki Ishii, Takuya Katagiri, Norihiro Tanahashi

    Journal of High Energy Physics2023 ( 6 )   19 6 2023

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

    Abstract

    We study hairy black holes in Einstein-Maxwell-complex scalar theory in four-dimensional asymptotically global anti-de Sitter (AdS) spacetime when the Robin boundary conditions are imposed on the scalar field. This setup is dual to the double trace deformation of strongly interacting field theory on R × S<sup>2</sup> by charged scalar operators. We identify the instability of the Reissner-Nordström-AdS (RNAdS) black holes under the Robin boundary conditions and construct backreacted geometries branching at the onset of the instability. Also considering associated horizonless geometries called boson stars, we obtain phase diagrams with fairly rich structure in the grand canonical ensemble depending on the boundary condition parameter or the deformation parameter, where phase transition occurs between thermal AdS, RNAdS, charged boson stars, and hairy black holes.

    DOI: 10.1007/jhep06(2023)106

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    Other Link: https://link.springer.com/article/10.1007/JHEP06(2023)106/fulltext.html

  • Superradiance and black resonator strings encounter helical black strings

    Óscar J. C. Dias, Takaaki Ishii, Keiju Murata, Jorge E. Santos, Benson Way

    Journal of High Energy Physics2023 ( 5 )   5 5 2023

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

    Abstract

    We construct a cohomogeneity-1 helical black string in six-dimensional Einstein gravity. The helical solution branches from the onset of the gravitational superradiant instability of the equal-spinning Myers-Perry black string. The isometry group of the helical black string is ℝ<sub>T</sub> × U(1)<sub>Z</sub> × SU(2), where the first two are helical isometries generated by linear combinations of time translation, shifts along the string, and rotation, each of which is individually broken by the superradiant instability. The helical black string is stationary, non-axisymmetric, and has nonzero horizon velocity despite the absence of momentum in the string direction. The entropy of the helical black string is higher than that of the Myers-Perry black string, but lower than cohomogeneity-2 “black resonator strings” (recently found) when the solutions overlap in the microcanonical ensemble. The entropy of the helical black string approaches zero when the horizon velocity along the string reaches its maximum given by the speed of light. Nevertheless, we find no evidence for the existence of regular horizonless solutions in this limit.

    DOI: 10.1007/jhep05(2023)041

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    Other Link: https://link.springer.com/article/10.1007/JHEP05(2023)041/fulltext.html

  • Gregory-Laflamme and superradiance encounter black resonator strings

    Óscar J. C. Dias, Takaaki Ishii, Keiju Murata, Jorge E. Santos, Benson Way

    Journal of High Energy Physics2023 ( 2 )   7 2 2023

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

    Abstract

    We construct novel black strings that are neither time-translation invariant, nor axisymmetric, nor translationally invariant in the string direction, but nevertheless have a helical Killing vector field. These solutions branch from the superradiant instability of D = 6 Myers-Perry black strings with equal angular momenta. We coin these solutions as black resonator strings and we find that they have more entropy than Myers-Perry black strings for the energies and angular momenta where both solutions coexist. We also construct Kaluza-Klein geons, which share the symmetries of black resonator strings, but are horizonless. Unlike in other superradiant systems, Kaluza-Klein geons are not the horizonless limit of black resonator strings and are instead entirely separate solutions.

    DOI: 10.1007/jhep02(2023)069

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    Other Link: https://link.springer.com/article/10.1007/JHEP02(2023)069/fulltext.html

  • Gregory-Laflamme encounters Superradiance

    Óscar J. C. Dias, Takaaki Ishii, Keiju Murata, Jorge E. Santos, Benson Way

    Journal of High Energy Physics2023 ( 1 )   25 1 2023

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

    Abstract

    We investigate the effect of superradiant scattering of gravitational perturbations on the stability of rotating black strings, focusing on the six dimensional equal-spinning Myers-Perry black string. We find that rapidly rotating black strings are unstable to gravitational superradiant modes within a bounded range of string lengths. The instability occurs because momentum along the string direction creates a potential barrier that allows for the confinement of superradiant modes. Yet, five dimensional Myers-Perry black holes do not have stable particle orbits so, unlike other known superradiant systems, these black strings remain stable to perturbations with sufficiently high azimuthal mode number — this is a ‘finite-m’ superradiant instability. For some parameters, this instability competes with the Gregory-Laflamme instability, but otherwise exists independently. The onset of this instability is degenerate and branches to multiple steady-state solutions. This paper is the first of a trilogy: in the next two, we construct two distinct families of rotating strings emerging from the superradiant onset (the ‘black resonator strings’ and ‘helical black strings’). We argue that similar physics is present in 5-dimensional Kerr black strings, but not in D &gt; 6 equal-spinning Myers-Perry black strings.

    DOI: 10.1007/jhep01(2023)147

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    Other Link: https://link.springer.com/article/10.1007/JHEP01(2023)147/fulltext.html

  • Energy extraction from AdS black holes via superradiance

    Takaaki Ishii, Youka Kaku, Keiju Murata

    Journal of High Energy Physics2022 ( 10 )   5 10 2022

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

    Abstract

    Superradiance is known as a wave amplification process caused by rotating or charged black holes. We argue that the superradiance of stationary black holes in asymptotically AdS spacetimes can be characterized by the ability of energy extraction. Specifically, we demonstrate that energy can be extracted from Reissner-Nordström-AdS<sub>4</sub> and Kerr-AdS<sub>4</sub> under appropriate time-dependent boundary conditions at conformal boundaries. This indicates that energy can be extracted from thermal states dual to these black holes by applying appropriate time-dependent sources. We also show that the energy extraction can be realized as a reversible process.

    DOI: 10.1007/jhep10(2022)024

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    Other Link: https://link.springer.com/article/10.1007/JHEP10(2022)024/fulltext.html

  • Chaotic string dynamics in deformed T1,1

    Takaaki Ishii, Shodai Kushiro, Kentaroh Yoshida

    Journal of High Energy Physics2021 ( 5 )   18 5 2021

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

    Abstract

    Recently, Arutyunov, Bassi and Lacroix have shown that 2D non-linear sigma model with a deformed T<sup>1,1</sup> background is classically integrable [arXiv:2010.05573 [hep-th]]. This background includes a Kalb-Ramond two-form with a critical value. Then the sigma model has been conjectured to be non-integrable when the two-form is off critical. We confirm this conjecure by explicitly presenting classical chaos. With a winding string ansatz, the system is reduced to a dynamical system described by a set of ordinary differential equations. Then we find classical chaos, which indicates non-integrability, by numerically computing Poincaré sections and Lyapunov spectra for some initial conditions.

    DOI: 10.1007/jhep05(2021)158

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    Other Link: https://link.springer.com/article/10.1007/JHEP05(2021)158/fulltext.html

  • Multioscillating black holes

    Takaaki Ishii, Keiju Murata, Jorge E. Santos, Benson Way

    Journal of High Energy Physics2021 ( 5 )   3 5 2021

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

    Abstract

    We study rotating global AdS solutions in five-dimensional Einstein gravity coupled to a multiplet complex scalar within a cohomogeneity-1 ansatz. The onset of the gravitational and scalar field superradiant instabilities of the Myers-Perry-AdS black hole mark bifurcation points to black resonators and hairy Myers-Perry-AdS black holes, respectively. These solutions are subject to the other (gravitational or scalar) instability, and result in hairy black resonators which contain both gravitational and scalar hair. The hairy black resonators have smooth zero-horizon limits that we call graviboson stars. In the hairy black resonator and graviboson solutions, multiple scalar components with different frequencies are excited, and hence these are multioscillating solutions. The phase structure of the solutions are examined in the microcanonical ensemble, i.e. at fixed energy and angular momenta. It is found that the entropy of the hairy black resonator is never the largest among them. We also find that hairy black holes with higher scalar wavenumbers are entropically dominant and occupy more of phase space than those of lower wavenumbers.

    DOI: 10.1007/jhep05(2021)011

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    Other Link: https://link.springer.com/article/10.1007/JHEP05(2021)011/fulltext.html

  • Resonating AdS soliton

    Markus Garbiso, Takaaki Ishii, Keiju Murata

    Journal of High Energy Physics2020 ( 8 )   26 8 2020

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

    Abstract

    The AdS soliton is a nonsingular spacetime that has a flat conformal boundary with a compact S<sup>1</sup> direction. We find a horizonless cohomogeneity-1 metric that describes nonlinear gravitational oscillations of the AdS soliton in five dimensions. We call this spacetime the resonating AdS soliton. This solution is obtained as the nonlinear extension of normal modes of the AdS soliton dual to spin-2 glueball excitations. The boundary energy momentum tensor of the resonating AdS soliton has time periodic components, and it is interpreted as a coherently excited state in the dual field theory. Physical quantities of the resonating AdS soliton are multivalued at a fixed energy, suggesting a transition between different frequency solutions. The energy of the resonating AdS soliton is higher than that of the undeformed AdS soliton, in accordance with the positive energy conjecture proposed by Horowitz and Myers.

    DOI: 10.1007/jhep08(2020)136

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    Other Link: https://link.springer.com/article/10.1007/JHEP08(2020)136/fulltext.html

  • Superradiant instability of black resonators and geons

    Takaaki Ishii, Keiju Murata, Jorge E. Santos, Benson Way

    Journal of High Energy Physics2020 ( 7 )   28 7 2020

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

    Abstract

    Black resonators and geons in global AdS are rapidly rotating, low-energy solutions with a helical Killing field. We study the linear mode stability of equal angular momenta, five-dimensional black resonators and geons under scalar, electromagnetic, and gravitational perturbations. We find that black resonators are unstable to the superradiant instability, in agreement with previously known results. Perhaps surprisingly, many geons appear linearly stable, despite having an ergoregion. This apparent stability implies that geons are important long-lived, low-energy states in the dual gauge theory. However, we do find that geons are unstable within a certain range of parameter space. We comment on the nature of this instability and to its possible endpoints. We also report on new non-spinning oscillating geons, which we construct within a cohomogeneity two ansatz. Given the existing arguments that suggest our linear stability results may be extended nonlinearly, our findings indicate that most geons are generic and long-lived solutions.

    DOI: 10.1007/jhep07(2020)206

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    Other Link: https://link.springer.com/article/10.1007/JHEP07(2020)206/fulltext.html

  • Large N analysis of $$ T\overline{T} $$-deformation and unavoidable negative-norm states

    Junichi Haruna, Takaaki Ishii, Hikaru Kawai, Katsuta Sakai, Kentaroh Yoshida

    Journal of High Energy Physics2020 ( 4 )   21 4 2020

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

    DOI: 10.1007/jhep04(2020)127

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  • Photonic black resonators and photon stars in AdS<sub>5</sub>

    Takaaki Ishii, Keiju Murata

    Classical and Quantum Gravity37 ( 7 ) 075009 - 075009   3 3 2020

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

    DOI: 10.1088/1361-6382/ab7418

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    Other Link: https://iopscience.iop.org/article/10.1088/1361-6382/ab7418/pdf

  • Gravitational perturbations as TTbar-deformations in 2D dilaton gravity systems

    Takaaki Ishii, Suguru Okumura, Jun-ichi Sakamoto, Kentaroh Yoshida

    Nuclear Physics B951   114901 - 114901   2 2020

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    Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.nuclphysb.2019.114901

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  • Cool baryon and quark matter in holographic QCD

    Takaaki Ishii, Matti Järvinen, Govert Nijs

    Journal of High Energy Physics2019 ( 7 )   1 7 2019

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

    Abstract

    We establish a holographic bottom-up model which covers both the baryonic and quark matter phases in cold and dense QCD. This is obtained by including the baryons using simple approximation schemes in the V-QCD model, which also includes the backreaction of the quark matter to the dynamics of pure Yang-Mills. We examine two approaches for homogeneous baryon matter: baryons as a thin layer of noninteracting matter in the holographic bulk, and baryons with a homogeneous bulk gauge field. We find that the second approach exhibits phenomenologically reasonable features. At zero temperature, the vacuum, baryon, and quark matter phases are separated by strongly first order transitions as the chemical potential varies. The equation of state in the baryonic phase is found to be stiff, i.e., the speed of sound clearly exceeds the value c<sub>s</sub><sup>2</sup> = 1/3 of conformal plasmas at high baryon densities.

    DOI: 10.1007/jhep07(2019)003

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    Other Link: https://link.springer.com/article/10.1007/JHEP07(2019)003/fulltext.html

  • Black resonators and geons in AdS <sub>5</sub>

    Takaaki Ishii, Keiju Murata

    Classical and Quantum Gravity36 ( 12 ) 125011 - 125011   29 5 2019

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

    DOI: 10.1088/1361-6382/ab1d76

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    Other Link: https://iopscience.iop.org/article/10.1088/1361-6382/ab1d76/pdf

  • Floquet superconductor in holography

    Takaaki Ishii, Keiju Murata

    Physical Review D98 ( 12 )   11 12 2018

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

    DOI: 10.1103/physrevd.98.126005

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.98.126005/fulltext

  • Holographic heavy-ion collisions: Analytic solutions with longitudinal flow, elliptic flow and vorticity

    Hans Bantilan, Takaaki Ishii, Paul Romatschke

    Physics Letters B785   201 - 206   10 2018

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    Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.physletb.2018.08.038

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  • Fate of chaotic strings in a confining geometry

    Takaaki Ishii, Keiju Murata, Kentaroh Yoshida

    Physical Review D95 ( 6 )   31 3 2017

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

    DOI: 10.1103/physrevd.95.066019

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    Other Link: http://link.aps.org/article/10.1103/PhysRevD.95.066019

  • Thermalization and confinement in strongly coupled gauge theories

    Takaaki Ishii, Elias Kiritsis, Christopher Rosen

    EPJ Web of Conferences126   02018 - 02018   4 11 2016

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    Publishing type:Research paper (scientific journal)   Publisher:EDP Sciences  

    DOI: 10.1051/epjconf/201612602018

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  • Time-dependence of the holographic spectral function: diverse routes to thermalisation

    Souvik Banerjee, Takaaki Ishii, Lata Kh Joshi, Ayan Mukhopadhyay, P. Ramadevi

    Journal of High Energy Physics2016 ( 8 )   8 8 2016

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

    DOI: 10.1007/jhep08(2016)048

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    Other Link: http://link.springer.com/content/pdf/10.1007/JHEP08(2016)048.pdf

  • Notes on frequencies and timescales in nonequilibrium Green's functions

    Takaaki Ishii

        26 5 2016

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    We discuss the ringdown behavior of the nonequilibrium Green's function in a
    strongly coupled theory with the holographic dual with a focus on
    quasinormal-mode equilibration. We study the time resolved spectral function
    for a probe scalar in Vaidya-AdS spacetime in detail as a complement to the
    preceding work arXiv:1603.06935 using further numerical results in very
    nonadiabatic temperature changes. It is shown that the relaxation of the
    nonequilibrium spectral function obtained through the Wigner transform is
    governed by the lowest quasinormal mode frequency. The timescale of the
    background temperature change is also observed in the frequency analysis. We
    then consider a toy model motivated by the quasinormal mode behavior and
    discuss these main features in numerical results are simply realized.

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    Other Link: http://arxiv.org/pdf/1605.08387v2

  • Dynamical AdS strings across horizons

    Takaaki Ishii, Keiju Murata

    Journal of High Energy Physics2016 ( 3 )   7 3 2016

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

    DOI: 10.1007/jhep03(2016)035

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  • Thermalization in a holographic confining gauge theory

    Takaaki Ishii, Elias Kiritsis, Christopher Rosen

    Journal of High Energy Physics2015 ( 8 )   3 8 2015

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

    Abstract

    Time dependent perturbations of states in the holographic dual of a 3+1 dimensional confining theory are considered. The perturbations are induced by varying the coupling to the theory’s most relevant operator. The dual gravitational theory belongs to a class of Einstein-dilaton theories which exhibit a mass gap at zero temperature and a first order deconfining phase transition at finite temperature. The perturbation is realized in various thermal bulk solutions by specifying time dependent boundary conditions on the scalar, and we solve the fully backreacted Einstein-dilaton equations of motion subject to these boundary conditions. We compute the characteristic time scale of many thermalization processes, noting that in every case we examine, this time scale is determined by the imaginary part of the lowest lying quasi-normal mode of the final state black brane. We quantify the dependence of this final state on parameters of the quench, and construct a dynamical phase diagram. Further support for a universal scaling regime in the abrupt quench limit is provided.

    DOI: 10.1007/jhep08(2015)008

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    Other Link: https://link.springer.com/content/pdf/10.1007/JHEP08(2015)008.pdf

  • Turbulent strings in AdS/CFT

    Takaaki Ishii, Keiju Murata

    Journal of High Energy Physics2015 ( 6 )   15 6 2015

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

    DOI: 10.1007/jhep06(2015)086

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    Other Link: http://link.springer.com/content/pdf/10.1007/JHEP06(2015)086.pdf

  • A simple holographic model of a charged lattice

    Francesco Aprile, Takaaki Ishii

    Journal of High Energy Physics2014 ( 10 )   27 10 2014

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

    DOI: 10.1007/jhep10(2014)151

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    Other Link: http://link.springer.com/content/pdf/10.1007/JHEP10(2014)151.pdf

  • Dynamical meson melting in holography

    Takaaki Ishii, Shunichiro Kinoshita, Keiju Murata, Norihiro Tanahashi

    Journal of High Energy Physics2014 ( 4 )   14 4 2014

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

    DOI: 10.1007/jhep04(2014)099

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  • Impurity effect in a holographic superconductor

    Takaaki Ishii, Sang-Jin Sin

    Journal of High Energy Physics2013 ( 4 )   22 4 2013

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

    DOI: 10.1007/jhep04(2013)128

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    Other Link: http://link.springer.com/article/10.1007/JHEP04(2013)128/fulltext.html

  • Long-distance properties of baryons in the Sakai–Sugimoto model

    Aleksey Cherman, Takaaki Ishii

    Physical Review D86 ( 4 )   2 8 2012

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

    DOI: 10.1103/physrevd.86.045011

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.86.045011/fulltext

  • Anomaly-induced charges in baryons

    Minoru Eto, Koji Hashimoto, Hideaki Iida, Takaaki Ishii, Yu Maezawa

    Physical Review D85 ( 11 )   21 6 2012

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

    DOI: 10.1103/physrevd.85.114038

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.85.114038/fulltext

  • Flows to Schrödinger geometries

    Takaaki Ishii, Tatsuma Nishioka

    Physical Review D84 ( 12 )   8 12 2011

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

    DOI: 10.1103/physrevd.84.125007

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    Other Link: http://link.aps.org/article/10.1103/PhysRevD.84.125007

  • Anomaly-induced charges in nucleons

    Minoru Eto, Koji Hashimoto, Hideaki Iida, Takaaki Ishii, Yu Maezawa

        28 3 2011

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    We show a novel charge structure of baryons in electromagnetic field due to
    the chiral anomaly. A key connection is to treat baryons as solitons of mesons.
    We use Skyrmions to calculate the charge distributions in a single nucleon and
    find an additional charge. We also perform calculations of charge distribution
    for classical multi-baryons with B=2, 3,...,8 and 17; they show amusing charge
    distributions.

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    Other Link: http://arxiv.org/pdf/1103.5443v2

  • Toward bound-state approach to strangeness in holographic QCD

    Takaaki Ishii

    Physics Letters B695 ( 1-4 ) 392 - 396   1 2011

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    Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.physletb.2010.11.043

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  • Three-flavor quark mass dependence of baryon spectra in holographic QCD

    Koji Hashimoto, Norihiro Iizuka, Takaaki Ishii, Daisuke Kadoh

    Physics Letters B691 ( 1 ) 65 - 71   7 2010

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    Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.physletb.2010.06.008

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  • N=4 super Yang-Mills theory from the plane wave matrix model

    Takaaki Ishii, Goro Ishiki, Shinji Shimasaki, Asato Tsuchiya

    Physical Review D78 ( 10 )   3 11 2008

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

    DOI: 10.1103/physrevd.78.106001

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.78.106001/fulltext

  • Fiber bundles and matrix models

    Takaaki Ishii, Goro Ishiki, Shinji Shimasaki, Asato Tsuchiya

    Physical Review D77 ( 12 )   20 6 2008

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

    DOI: 10.1103/physrevd.77.126015

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.77.126015/fulltext

  • On Relationships among Chern-Simons Theory, BF Theory and Matrix Model

    T. Ishii, G. Ishiki, K. Ohta, S. Shimasaki, A. Tsuchiya

    Progress of Theoretical Physics119 ( 5 ) 863 - 882   1 5 2008

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

    DOI: 10.1143/ptp.119.863

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  • T-duality, fiber bundles and matrices

    Takaaki Ishii, Goro Ishiki, Shinji Shimasaki, Asato Tsuchiya

    Journal of High Energy Physics2007 ( 05 ) 014 - 014   8 5 2007

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

    DOI: 10.1088/1126-6708/2007/05/014

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Research Projects

  • 拡張されたブラックホールで探るゲージ理論の新しい相構造

    日本学術振興会  科学研究費助成事業 

    石井 貴昭

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    4 2019 - 3 2023

    Grant number:19K03871

    Grant amount:\4290000 ( Direct Cost: \3300000 、 Indirect Cost:\990000 )

    前年度まではAdS時空における超放射不安定性に焦点を置いてきた。というのも、AdS時空の大域的な構造により波が時空に閉じ込められることが不安定性を引き起こすのに重要な役割を果たしたからである。しかしながら、波の閉じ込めのメカニズムがあれば必ずしもAdS時空でなくても不安定性が起こる可能性がある。この可能性を持つ時空として本年度はブラックストリング時空に注目し、とりわけ特定の高次元ブラックストリング時空に注目した解析において超放射不安定性が起こることを新たに発見した。先行研究では5次元以下のブラックストリングでの不安定性が議論されていたが、高次元に関しては否定的な結果がいくつか知られていただけだった。それに対して、本研究では6次元ブラックストリングについて、特定の重力場の摂動に注目することで不安定性を見出すことに成功した。また、スカラー場やマクスウェル場などの他の摂動については先行研究と整合的に安定であることも追検証し、本研究で注目する重力場の摂動が例外的であることが分かった。そして、これまでの共鳴ブラックホールでの知見と同様に、ここで見つかった不安定性からも共鳴ブラックストリングと呼ばれるべき変形されたブラックホール解が得られることがわかった。
    AdS時空でも、荷電ブラックホールの超放射不安定性に関して、Robin境界条件と呼ばれる一般的な境界条件に関する先行研究に触発されて、その不安定性から出現するhairyブラックホール解を構成する共同研究をその著者らと新しく立ち上げた。この研究では、AdS時空の荷電ブラックホールに対して考えられるAdSマクスウェルヒッグス理論において、最も一般的な境界条件を持つhairyブラックホール解が得られることがわかった。

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  • 行列模型による非摂動的解析に基づくAdS/CFT対応及びM理論の研究

    日本学術振興会  科学研究費助成事業 

    石井 貴昭

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    2009 - 2010

    Grant number:09J02062

    Grant amount:\1400000 ( Direct Cost: \1400000 )

    酒井杉本模型をクォーク質量も取り込んだ定式化で成功させることは挑戦的な課題である。この模型はカイラル対称性との相性がよく、素朴にはクォーク質量がゼロのQCDの重力双対である。しかし、現実のQCDを意識した場合にはクォーク質量がある場合も扱えることが望まれる。とくにストレンジクォークはQCDで質量がゼロでないとして扱われるべきで注目に値する。ここを調べるにはメソンではなくバリオンから始める効果的であると考えられ、このような動機から、私は酒井杉本模型でストレンジネスを含むバリオンの研究に取り組んだ。論文「Toward Bound-State Approach to Strangeness in Holographic QCD」では束縛状態方法という手法を酒井杉本模型において考察した。この方法ではストレンジクォークは十分重いとみなし、SU(3)フレーバー対称性を捨ててu, dのみを含むバリオンとKメソンとの束縛状態としてハイペロンを実現する。これは元々Skyrme模型で考案された方法で、そこではなかなかうまく行っている。しかしながら、今回の結果ではSkyrme模型と状況が異なり、酒井杉本模型では束縛しにくいという結果が得られた。素朴な解釈としては束縛状態方法でメソンとバリオンとを並列に考える際にこれら二つの模型は似て非なるものであり、とくにSkyrmionと酒井杉本模型でのインスタントン的バリオンとの差異が影響していると考えられる。その一方で、今回の模型で自然に実現される有効的なKメソン質量について、バリオンの中心に近い所で減少するという非自明な振る舞いが得られた。

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