Updated on 2024/10/07

写真b

 
UGAJIN Tomonori
 
*Items subject to periodic update by Rikkyo University (The rest are reprinted from information registered on researchmap.)
Affiliation*
College of Science Department of Physics
Graduate School of Science Doctoral Program in Physics
Graduate School of Science Master's Program in Physics
Title*
Associate Professor
Research Theme*
  • 素粒子論、特に超弦理論の重力の量子論としての側面に興味を持っている。最近ではAdS/CFT対応などのホログラフィー原理が成り立つ機構、ブラックホール内部の再構成問題、ドシッター空間の微視的構造等の重力の量子効果が顕著な系における物理現象を、量子情報理論を用いて研究している。

  • Research Interests
  • 量子情報理論

  • ホログラフィー原理

  • 超弦理論

  • Campus Career*
    • 9 2023 - Present 
      College of Science   Department of Physics   Associate Professor
    • 9 2023 - Present 
      Graduate School of Science   Master's Program in Physics   Associate Professor
    • 9 2023 - Present 
      Graduate School of Science   Doctoral Program in Physics   Associate Professor
     

    Research Areas

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

    Research History

    • 9 2023 - Present 
      Rikkyo University   College of Science Department of Physics

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    • 4 2020 - 9 2023 
      Kyoto University

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      Country:United States

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    • 9 2019 - 3 2020 
      ペンシルバニア大学   物理学科   博士研究員

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      Country:United States

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    • 9 2017 - 8 2019 
      沖縄科学技術大学院大学   博士研究員

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      Country:Japan

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    • 9 2014 - 8 2017 
      カリフォルニア大学サンタバーバラ校   カブリ理論物理学研究所   博士研究員

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      Country:United States

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    • 4 2014 - 8 2014 
      The University of Tokyo   Graduate School of Science

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    • 4 2012 - 3 2014 
      The University of Tokyo   Graduate School of Science

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    Education

    • 4 2009 - 3 2014 
      The University of Tokyo   Graduate School of Science   Department of Physics

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    Awards

    • 10 2018  
      日本物理学会  若手奨励賞(素粒子論領域) 

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    Papers

    • Holographic local operator quenches in BCFTs

      Taishi Kawamoto, Takato Mori, Yu ki Suzuki, Tadashi Takayanagi, Tomonori Ugajin

      Journal of High Energy Physics2022 ( 5 )   5 2022

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      Publishing type:Research paper (scientific journal)  

      We present a gravity dual of local operator quench in a two-dimensional CFT with conformal boundaries. This is given by a massive excitation in a three-dimensional AdS space with the end of the world brane (EOW brane). Due to the gravitational backreaction, the EOW brane gets deformed in a nontrivial way. We show that the energy-momentum tensor and entanglement entropy computed from the gravity dual and from the BCFT in the large c limit match perfectly. Interestingly, this comparison avoids the folding of the EOW brane in an elegant way.

      DOI: 10.1007/JHEP05(2022)060

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    • A comment on a fine-grained description of evaporating black holes with baby universes

      Iizuka, Norihiro, Miyata, Akihiro, Ugajin, Tomonori

      JHEP09   158 - 158   2022

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      Publishing type:Research paper (scientific journal)  

      DOI: 10.1007/JHEP09(2022)158

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    • Product of random states and spatial (half-)wormholes

      Kanato Goto, Yuya Kusuki, Kotaro Tamaoka, Tomonori Ugajin

      Journal of High Energy Physics2021 ( 10 )   10 2021

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

      Abstract

      We study how coarse-graining procedure of an underlying UV-complete quantum gravity gives rise to a connected geometry. It has been shown, quantum entanglement plays a key role in the emergence of such a geometric structure, namely a smooth Einstein-Rosen bridge. In this paper, we explore the possibility of the emergence of similar geometric structure from classical correlation, in the AdS/CFT setup. To this end, we consider a setup where we have two decoupled CFT Hilbert spaces, then choose a random typical state in one of the Hilbert spaces and the same state in the other. The total state in the fine-grained picture is of course a tensor product state, but averaging over the states sharing the same random coefficients creates a geometric connection for simple probes. Then, the apparent spatial wormhole causes a factorization puzzle. We argue that there is a spatial analog of half-wormholes, which resolves the puzzle in the similar way as the spacetime half-wormholes.

      DOI: 10.1007/jhep10(2021)205

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      Other Link: https://link.springer.com/article/10.1007/JHEP10(2021)205/fulltext.html

    • Quantum Field Theory and Quantum Information―Relative Entropy and Its Application Peer-reviewed

      Ugajin Tomonori, Nishioka Tatsuma

      Butsuri76 ( 07 ) 435 - 443   7 2021

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      Language:Japanese   Publisher:The Physical Society of Japan  

      <p>Quantum information theory has been successfully applied to various fields of fundamental physics. Relative entropy is one of the central concepts of quantum information theory, which defines a distance measure with nice properties in the space of density matrices. In this article, we review selected examples of the applications of relative entropy to high energy physics, quantum theory of gravity, and nonequilibrium physics.</p>

      DOI: 10.11316/butsuri.76.7_435

      CiNii Article

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    • Spectrum of end of the world branes in holographic BCFTs Peer-reviewed

      Masamichi Miyaji, Tadashi Takayanagi, Tomonori Ugajin

      Journal of High Energy Physics2021 ( 6 )   6 2021

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

      <title>A<sc>bstract</sc>
      </title>We study overlaps between two regularized boundary states in conformal field theories. Regularized boundary states are dual to end of the world branes in an AdS black hole via the AdS/BCFT. Thus they can be regarded as microstates of a single sided black hole. Owing to the open-closed duality, such an overlap between two different regularized boundary states is exponentially suppressed as <inline-formula><alternatives><tex-math>$$ \left\langle \left.{\psi}_a\right|{\psi}_b\right\rangle \sim {e}^{-O\left({h}_{ab}^{\left(\min \right)}\right)} $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
      <mml:mfenced>
      <mml:mrow>
      <mml:mfenced>
      <mml:msub>
      <mml:mi>ψ</mml:mi>
      <mml:mi>a</mml:mi>
      </mml:msub>
      </mml:mfenced>
      <mml:msub>
      <mml:mi>ψ</mml:mi>
      <mml:mi>b</mml:mi>
      </mml:msub>
      </mml:mrow>
      </mml:mfenced>
      <mml:mo>∼</mml:mo>
      <mml:msup>
      <mml:mi>e</mml:mi>
      <mml:mrow>
      <mml:mo>−</mml:mo>
      <mml:mi>O</mml:mi>
      <mml:mfenced>
      <mml:msubsup>
      <mml:mi>h</mml:mi>
      <mml:mi>ab</mml:mi>
      <mml:mfenced>
      <mml:mo>min</mml:mo>
      </mml:mfenced>
      </mml:msubsup>
      </mml:mfenced>
      </mml:mrow>
      </mml:msup>
      </mml:math></alternatives></inline-formula>, where <inline-formula><alternatives><tex-math>$$ {h}_{ab}^{\left(\min \right)} $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
      <mml:msubsup>
      <mml:mi>h</mml:mi>
      <mml:mi>ab</mml:mi>
      <mml:mfenced>
      <mml:mo>min</mml:mo>
      </mml:mfenced>
      </mml:msubsup>
      </mml:math></alternatives></inline-formula> is the lowest energy of open strings which connect two different boundaries <italic>a</italic> and <italic>b</italic>. Our gravity dual analysis leads to <inline-formula><alternatives><tex-math>$$ {h}_{ab}^{\left(\min \right)} $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
      <mml:msubsup>
      <mml:mi>h</mml:mi>
      <mml:mi>ab</mml:mi>
      <mml:mfenced>
      <mml:mo>min</mml:mo>
      </mml:mfenced>
      </mml:msubsup>
      </mml:math></alternatives></inline-formula> = <italic>c/</italic>24 for a pure AdS<sub>3</sub> gravity. This shows that a holographic boundary state is a random vector among all left-right symmetric states, whose number is given by a square root of the number of all black hole microstates. We also perform a similar computation in higher dimensions, and find that <inline-formula><alternatives><tex-math>$$ {h}_{ab}^{\left(\min \right)} $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
      <mml:msubsup>
      <mml:mi>h</mml:mi>
      <mml:mi>ab</mml:mi>
      <mml:mfenced>
      <mml:mo>min</mml:mo>
      </mml:mfenced>
      </mml:msubsup>
      </mml:math></alternatives></inline-formula> depends on the tensions of the branes. In our analysis of holographic boundary states, the off diagonal elements of the inner products can be computed directly from on-shell gravity actions, as opposed to earlier calculations of inner products of microstates in two dimensional gravity.

      DOI: 10.1007/jhep06(2021)023

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      Other Link: https://link.springer.com/article/10.1007/JHEP06(2021)023/fulltext.html

    • Entanglement between two gravitating universes

      Vijay Balasubramanian, Arjun Kar, Tomonori Ugajin

          27 4 2021

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      We study two disjoint universes in an entangled pure state. When only one
      universe contains gravity, the path integral for the $n^{\text{th } }$ R\'enyi
      entropy includes a wormhole between the $n$ copies of the gravitating universe,
      leading to a standard "island formula" for entanglement entropy consistent with
      unitarity of quantum information. When both universes contain gravity,
      gravitational corrections to this configuration lead to a violation of
      unitarity. However, the path integral is now dominated by a novel wormhole with
      $2n$ boundaries connecting replica copies of both universes. The analytic
      continuation of this contribution involves a quotient by $\mathbb{Z}_n$ replica
      symmetry, giving a cylinder connecting the two universes. When entanglement is
      large, this configuration has an effective description as a "swap wormhole", a
      geometry in which the boundaries of the two universes are glued together by a
      "swaperator". This description allows precise computation of a generalized
      entropy-like formula for entanglement entropy. The quantum extremal surface
      computing the entropy lives on the Lorentzian continuation of the cylinder/swap
      wormhole, which has a connected Cauchy slice stretching between the universes
      -- a realization of the ER=EPR idea. The new wormhole restores unitarity of
      quantum information.

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      Other Link: http://arxiv.org/pdf/2104.13383v1

    • Evaporation of black holes in flat space entangled with an auxiliary universe

      Akihiro Miyata, Tomonori Ugajin

          1 4 2021

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      We study a thermofield double type entangled state on two disjoint universes
      $A$ and $B$, where one of the universes is asymptotically flat containing a
      black hole. As we increase the entanglement temperature, this black hole
      receives back-reaction from the stress energy tensor of the state. This results
      in lengthening of the wormhole region in the black hole interior, and
      decreasing of its horizon area, both of which are key features of an
      evaporating black hole. We then compute the entanglement entropy on the
      universe $A$ through the island formula, and argue that it naturally follows
      the Page curve of an evaporating black hole in flat space. We also study the
      effects of local operations in the gravitating universe with the black hole. We
      find that they accelerate the evaporation of the black hole, therefore disrupt
      the entanglement between two universes. Furthermore, we observe that depending
      on whether the operation can be regarded as an LOCC or not, the behavior of the
      entanglement entropy changes. In particular, when the operation is made neither
      in the entanglement wedge of the radiation system or that of the black hole,
      the transition between the island phase and the no-island phase can happen
      multiple times.

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      Other Link: http://arxiv.org/pdf/2104.00183v1

    • Wormholes and holographic decoherence Peer-reviewed

      Takanori Anegawa, Norihiro Iizuka, Kotaro Tamaoka, Tomonori Ugajin

      Journal of High Energy Physics2021 ( 3 )   3 2021

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

      <title>A<sc>bstract</sc>
      </title>We study a class of decoherence process which admits a 3 dimensional holographic bulk. Starting from a thermo-field double dual to a wormhole, we prepare another thermo-field double which plays the role of environment. By allowing the energy flow between the original and environment thermo-field double, the entanglement of the original thermo-field double eventually decoheres. We model this decoherence by four-boundary wormhole geometries, and study the time-evolution of the moduli parameters to see the change of the entanglement pattern among subsystems. A notable feature of this holographic decoherence processes is that at the end point of the processes, the correlations of the original thermo-field double are lost completely both classically and also quantum mechanically. We also discuss distinguishability between thermo-field double state and thermo mixed double state, which contains only classical correlations, and construct a code subspace toy model for that.

      DOI: 10.1007/jhep03(2021)214

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      Other Link: http://link.springer.com/article/10.1007/JHEP03(2021)214/fulltext.html

    • Islands in de Sitter space Peer-reviewed

      Vijay Balasubramanian, Arjun Kar, Tomonori Ugajin

      Journal of High Energy Physics2021 ( 2 )   2 2021

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

      <title>A<sc>bstract</sc>
      </title>We consider black holes in 2d de Sitter JT gravity coupled to a CFT, and entangled with matter in a disjoint non-gravitating universe. Tracing out the entangling matter leaves the CFT in a density matrix whose stress tensor backreacts on the de Sitter geometry, lengthening the wormhole behind the black hole horizon. Naively, the entropy of the entangling matter increases without bound as the strength of the entanglement increases, but the monogamy property predicts that this growth must level off. We compute the entropy via the replica trick, including wormholes between the replica copies of the de Sitter geometry, and find a competition between conventional field theory entanglement entropy and the surface area of extremal “islands” in the de Sitter geometry. The black hole and cosmological horizons both play a role in generating such islands in the backreacted geometry, and have the effect of stabilizing the entropy growth as required by monogamy. We first show this in a scenario in which the de Sitter spatial section has been decompactified to an interval. Then we consider the compact geometry, and argue for a novel interpretation of the island formula in the context of closed universes that recovers the Page curve. Finally, we comment on the application of our construction to the cosmological horizon in empty de Sitter space.

      DOI: 10.1007/jhep02(2021)072

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      Other Link: http://link.springer.com/article/10.1007/JHEP02(2021)072/fulltext.html

    • Geometric secret sharing in a model of Hawking radiation Peer-reviewed

      Vijay Balasubramanian, Arjun Kar, Onkar Parrikar, Gábor Sárosi, Tomonori Ugajin

      Journal of High Energy Physics2021 ( 1 )   1 2021

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

      <title>A<sc>bstract</sc>
      </title>We consider a black hole in three dimensional AdS space entangled with an auxiliary radiation system. We model the microstates of the black hole in terms of a field theory living on an end of the world brane behind the horizon, and allow this field theory to itself have a holographic dual geometry. This geometry is also a black hole since entanglement of the microstates with the radiation leaves them in a mixed state. This “inception black hole” can be purified by entanglement through a wormhole with an auxiliary system which is naturally identified with the external radiation, giving a realization of the ER=EPR scenario. In this context, we propose an extension of the Ryu-Takayanagi (RT) formula, in which extremal surfaces computing entanglement entropy are allowed to pass through the brane into its dual geometry. This new rule reproduces the Page curve for evaporating black holes, consistently with the recently proposed “island formula”. We then separate the radiation system into pieces. Our extended RT rule shows that the entanglement wedge of the union of radiation subsystems covers the black hole interior at late times, but the union of entanglement wedges of the subsystems may not. This result points to a secret sharing scheme in Hawking radiation wherein reconstruction of certain regions in the interior is impossible with any subsystem of the radiation, but possible with all of it.

      DOI: 10.1007/jhep01(2021)177

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      Other Link: https://link.springer.com/article/10.1007/JHEP01(2021)177/fulltext.html

    • Holographic Rényi relative divergence in JT gravity Peer-reviewed

      Tomonori Ugajin

      Journal of High Energy Physics (JHEP)2021 ( 5 )   11 11 2020

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      We holographically compute the R\'enyi relative divergence $D_{\alpha}
      (\rho_{+} || \rho_{-})$ between two density matrices $\rho_{+}, \; \rho_{-}$
      prepared by path integrals with constant background fields $\lambda_{\pm}$
      coupled to a marginal operator in JT gravity. Our calculation is non
      perturbative in the difference between two sources $ \lambda_{+} -\lambda_{-}$.
      When this difference is large, the bulk geometry becomes a black hole with the
      maximal temperature allowed by the R\'enyi index $\alpha$. In this limit, we
      find an analytic expression of the R\'enyi relative divergence, which is given
      by the on shell action of the back reacted black hole plus the contribution
      coming from the discontinuous change of the background field.

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      Other Link: http://arxiv.org/pdf/2011.05539v1

    • Spin structures and baby universes Peer-reviewed

      Vijay Balasubramanian, Arjun Kar, Simon F. Ross, Tomonori Ugajin

      Journal of High Energy Physics2020 ( 9 )   9 2020

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

      <title>A<sc>bstract</sc>
      </title>We extend a 2d topological model of the gravitational path integral to include sums over spin structure, corresponding to Neveu-Schwarz (NS) or Ramond (R) boundary conditions for fermions. This path integral corresponds to a correlator of boundary creation operators on a non-trivial baby universe Hilbert space, and vanishes when the number of R boundaries is odd. This vanishing implies a non-factorization of the correlator, which necessitates a dual interpretation of the bulk path integral in terms of a product of partition functions (associated to NS boundaries) and Witten indices (associated to R boundaries), averaged over an ensemble of theories with varying Hilbert space dimension and different numbers of bosonic and fermionic states. We also consider a model with End-of-the-World (EOW) branes, for which the dual ensemble then includes a sum over randomly chosen fermionic and bosonic states. We propose two modifications of the bulk path integral which restore an interpretation in a single dual theory: (i) a geometric prescription where we add extra boundaries with a sum over their spin structures, and (ii) an algebraic prescription involving “spacetime D-branes”. We extend our ideas to Jackiw-Teitelboim gravity, and propose a dual description of a single unitary theory with spin structure in a system with eigenbranes.

      DOI: 10.1007/jhep09(2020)192

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      Other Link: http://link.springer.com/article/10.1007/JHEP09(2020)192/fulltext.html

    • Entanglement between two disjoint universes Peer-reviewed

      Vijay Balasubramanian, Arjun Kar, Tomonori Ugajin

      Journal of High Energy Physics (JHEP)02 (2021)   12 8 2020

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      We use the replica method to compute the entanglement entropy of a universe
      without gravity entangled in a thermofield-double-like state with a disjoint
      gravitating universe. Including wormholes between replicas of the latter gives
      an entropy functional which includes an "island" on the gravitating universe.
      We solve the back-reaction equations when the cosmological constant is negative
      to show that this island coincides with a causal shadow region that is created
      by the entanglement in the gravitating geometry. At high entanglement
      temperatures, the island contribution to the entropy functional leads to a
      bound on entanglement entropy, analogous to the Page behavior of evaporating
      black holes. We demonstrate that the entanglement wedge of the non-gravitating
      universe grows with the entanglement temperature until, eventually, the
      gravitating universe can be entirely reconstructed from the non-gravitating
      one.

      DOI: 10.1007/JHEP02(2021)136

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      Other Link: http://arxiv.org/pdf/2008.05274v2

    • Perturbative expansions of Rényi relative divergences and holography Peer-reviewed

      Tomonori Ugajin

      Journal of High Energy Physics2020 ( 6 )   6 2020

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

      DOI: 10.1007/jhep06(2020)053

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    • Towards an entanglement measure for mixed states in CFTs based on relative entropy Peer-reviewed

      Tadashi Takayanagi, Tomonori Ugajin, Koji Umemoto

      Journal of High Energy Physics2018 ( 10 )   10 2018

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

      Relative entropy of entanglement (REE) is an entanglement measure of bipartite mixed states, defined by the minimum of the relative entropy S((AB) ||sigma(AB) ) between a given mixed state (AB) and an arbitrary separable state sigma(AB) . The REE is always bounded by the mutual information I-AB = S((AB) ||(A) circle times (B)) because the latter measures not only quantum entanglement but also classical correlations. In this paper we address the question of to what extent REE can be small compared to the mutual information in conformal field theories (CFTs). For this purpose, we perturbatively compute the relative entropy between the vacuum reduced density matrix AB0 on disjoint subsystems A B and arbitrarily separable state sigma(AB) in the limit where two subsystems A and B are well separated, then minimize the relative entropy with respect to the separable states. We argue that the result highly depends on the spectrum of CFT on the subsystems. When we have a few low energy spectrum of operators as in the case where the subsystems consist of finite number of spins in spin chain models, the REE is considerably smaller than the mutual information. However in general our perturbative scheme breaks down, and the REE can be as large as the mutual information.

      DOI: 10.1007/jhep10(2018)166

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    • Chaos and relative entropy Peer-reviewed

      Yuya O. Nakagawa, Gábor Sárosi, Tomonori Ugajin

      Journal of High Energy Physics2018 ( 7 )   7 2018

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

      DOI: 10.1007/jhep07(2018)002

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    • Modular Hamiltonians of excited states, OPE blocks and emergent bulk fields Peer-reviewed

      Gábor Sárosi, Tomonori Ugajin

      Journal of High Energy Physics2018 ( 1 )   1 2018

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

      DOI: 10.1007/jhep01(2018)012

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    • Mutual information of excited states and relative entropy of two disjoint subsystems in CFT Peer-reviewed

      Tomonori Ugajin

      Journal of High Energy Physics2017 ( 10 )   10 2017

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

      DOI: 10.1007/jhep10(2017)184

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    • Numerical calculations on the relative entanglement entropy in critical spin chains Peer-reviewed

      Yuya O Nakagawa, Tomonori Ugajin

      Journal of Statistical Mechanics: Theory and Experiment2017 ( 9 ) 093104 - 093104   22 9 2017

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

      DOI: 10.1088/1742-5468/aa85c1

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      Other Link: http://stacks.iop.org/1742-5468/2017/i=9/a=093104?key=crossref.fbdd76e38be70ea8b2541a39620c4fb9

    • (Non-adiabatic) string creation on nice slices in Schwarzschild black holes Peer-reviewed

      Andrea Puhm, Francisco Rojas, Tomonori Ugajin

      Journal of High Energy Physics2017 ( 4 )   4 2017

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

      DOI: 10.1007/jhep04(2017)156

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    • Relative entropy of excited states in conformal field theories of arbitrary dimensions Peer-reviewed

      Gábor Sárosi, Tomonori Ugajin

      Journal of High Energy Physics2017 ( 2 )   2 2017

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

      DOI: 10.1007/jhep02(2017)060

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    • Relative entropy of excited states in two dimensional conformal field theories Peer-reviewed

      Gábor Sárosi, Tomonori Ugajin

      Journal of High Energy Physics2016 ( 7 )   7 2016

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

      DOI: 10.1007/jhep07(2016)114

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    • Finite size effect on dynamical entanglement entropy: CFT and holography

      Gautam Mandal, Ritam Sinha, Tomonori Ugajin

          26 4 2016

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      Time-dependent entanglement entropy (EE) is computed for a single interval in
      two-dimensional conformal theories from a quenched initial state in the
      presence of spatial boundaries. The EE is found to be periodic in time with
      periodicity equal to the system size $L$. For large enough $L$, the EE shows a
      rise to a thermal value (characterized by a temperature $1/\beta$ determined by
      the initial state), followed by periodic returns to the original value. This
      works irrespective of whether the conformal field theory (CFT) is rational or
      irrational. For conformal field theories with a holographic dual, the large $c$
      limit plays an essential role in ensuring that the EE computed from the CFT is
      universal (independent of the details of the CFT and of boundary conditions)
      and is exactly matched by the holographic EE. The dual geometry is computed and
      it interpolates between a BTZ black hole at large $L$ and global AdS at large
      $\beta$.

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      Other Link: http://arxiv.org/pdf/1604.07830v1

    • Holographic entanglement and causal shadow in time-dependent Janus black hole Peer-reviewed

      Yūki Nakaguchi, Noriaki Ogawa, Tomonori Ugajin

      Journal of High Energy Physics2015 ( 7 )   7 2015

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

      DOI: 10.1007/jhep07(2015)080

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      Other Link: http://link.springer.com/content/pdf/10.1007/JHEP07(2015)080.pdf

    • Supersymmetric Rényi entropy in five dimensions Peer-reviewed

      Naofumi Hama, Tatsuma Nishioka, Tomonori Ugajin

      Journal of High Energy Physics2014 ( 12 )   12 2014

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

      DOI: 10.1007/jhep12(2014)048

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    • Two dimensional quantum quenches and holography

      Tomonori Ugajin

          11 11 2013

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      We propose a holographic realization of quantum quenches in two dimensional
      conformal field theories. In particular, we discuss time evolutions of
      holographic entanglement entropy in these backgrounds and compare them with CFT
      results. The key ingredient of the construction is an introduction of a
      spacetime boundary into bulk geometries, which is the gravity counterpart of a
      boundary state in the dual CFT. We consider several examples, including local
      quenches and an inhomogeneous quench which is dual to fusion of two black
      string into the third one.

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      Other Link: http://arxiv.org/pdf/1311.2562v1

    • An entropy formula for higher spin black holes via conical singularities Peer-reviewed

      Per Kraus, Tomonori Ugajin

      Journal of High Energy Physics2013 ( 5 )   5 2013

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

      DOI: 10.1007/jhep05(2013)160

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      Other Link: http://link.springer.com/article/10.1007/JHEP05(2013)160/fulltext.html

    • Thermodynamical Property of Entanglement Entropy for Excited States Peer-reviewed

      Jyotirmoy Bhattacharya, Masahiro Nozaki, Tadashi Takayanagi, Tomonori Ugajin

      Physical Review Letters110 ( 9 )   1 3 2013

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

      DOI: 10.1103/physrevlett.110.091602

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      Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.110.091602/fulltext

    • Central charges for BCFTs and holography Peer-reviewed

      Masahiro Nozaki, Tadashi Takayanagi, Tomonori Ugajin

      Journal of High Energy Physics2012 ( 6 )   6 2012

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

      DOI: 10.1007/jhep06(2012)066

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      Other Link: http://link.springer.com/article/10.1007/JHEP06(2012)066/fulltext.html

    • Soliton stars as holographic confined Fermi liquids Peer-reviewed

      Jyotirmoy Bhattacharya, Noriaki Ogawa, Tadashi Takayanagi, Tomonori Ugajin

      Journal of High Energy Physics2012 ( 2 )   2 2012

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

      In this paper, we study a holographic dual of a confined Fermi liquid state by putting a charged fluid of fermions in the AdS soliton geometry. This can be regarded as a confined analogue of electron stars. Depending on the parameters such as the mass and charge of the bulk fermion field, we found three different phase structures when we change the values of total charge density at zero temperature. In one of the three cases, our confined solution (called soliton star) is always stable and this solution approaches to the electron star away from the tip. In both the second and third case, we find a confinement/deconfinement phase transition. Moreover, in the third one, there is a strong indication that the soliton star decays into an inhomogeneous solution. We also analyze the probe fermion equations (in the WKB approximation) in the background of this soliton star geometry to confirm the presence of many Fermi-surfaces in the system.

      DOI: 10.1007/jhep02(2012)137

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      Other Link: http://link.springer.com/article/10.1007/JHEP02(2012)137/fulltext.html

    • Holographic Fermi surfaces and entanglement entropy Peer-reviewed

      Noriaki Ogawa, Tadashi Takayanagi, Tomonori Ugajin

      Journal of High Energy Physics2012 ( 1 )   1 2012

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

      We argue that Landau-Fermi liquids do not have any gravity duals in the purely classical limit. We employ the logarithmic behavior of entanglement entropy to characterize the existence of Fermi surfaces. By imposing the null energy condition, we show that the specific heat always behaves anomalously. We also present a classical gravity dual which has the expected behavior of the entanglement entropy and specific heat for non-Fermi liquids.

      DOI: 10.1007/jhep01(2012)125

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      Other Link: http://link.springer.com/article/10.1007/JHEP01(2012)125/fulltext.html

    • Holographic conductivity in disordered systems Peer-reviewed

      Shinsei Ryu, Tadashi Takayanagi, Tomonori Ugajin

      Journal of High Energy Physics2011 ( 4 )   4 2011

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

      DOI: 10.1007/jhep04(2011)115

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      Other Link: http://link.springer.com/article/10.1007/JHEP04(2011)115/fulltext.html

    • Measuring black hole formations by entanglement entropy via coarse-graining Peer-reviewed

      Tadashi Takayanagi, Tomonori Ugajin

      Journal of High Energy Physics2010 ( 11 )   11 2010

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

      We argue that the entanglement entropy offers us a useful coarse-grained entropy in time-dependent AdS/CFT. We show that the total von-Neumann entropy remains vanishing even when a black hole is created in a gravity dual, being consistent with the fact that its corresponding CFT is described by a time-dependent pure state. We analytically calculate the time evolution of entanglement entropy for a free Dirac fermion on a circle following a quantum quench. This is interpreted as a toy holographic dual of black hole creations and annihilations. It is manifestly free from the black hole information problem.

      DOI: 10.1007/jhep11(2010)054

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      Other Link: http://link.springer.com/article/10.1007/JHEP11(2010)054/fulltext.html

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    Research Projects

    • 量子情報を用いた量子ブラックホールの内部の物理学の解明

      日本学術振興会  科学研究費助成事業 

      飯塚 則裕, 宇賀神 知紀, 寺嶋 靖治, 野海 俊文, 重森 正樹

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      9 2021 - 3 2026

      Grant number:21H05184

      Grant amount:\76440000 ( Direct Cost: \58800000 、 Indirect Cost:\17640000 )

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    • 共形場理論における相対エントロピーとその様々な分野への応用

      日本学術振興会  科学研究費助成事業 

      宇賀神 知紀

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      3 2020 - 3 2025

      Grant number:19K14716

      Grant amount:\3250000 ( Direct Cost: \2500000 、 Indirect Cost:\750000 )

      量子エンタングルメントとブラックホール内部の関係性について研究した。特にブラックホールのアイランド公式は、ブラックホールの微視的な状態と、ホーキング放射の間の量子相関が、ブラックホール内部の時空構造を決定してしまうことを示唆する。その応用として、我々の最近の論文 では、二つの全く繋がりのないブラックホール A,B を用意し、それらの間の量子相関を大きくしていった場合に、(独立だった)A,B の内部がアインシュタインローゼン橋でつながることを、アイランド公式の観点から示した。このことは量子相関という情報理論的な概念が、アインシュタインローゼン橋という時空の幾何学的な構造と、一般相対論のダイナミクスを通じて直接対応していることを示している(ER = EPR対応)

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    • Higher spin black holeの研究

      日本学術振興会  科学研究費助成事業 

      宇賀神 知紀

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      2012 - 2013

      Grant number:12J09062

      Grant amount:\2000000 ( Direct Cost: \2000000 )

      higher spin理論は重力場とスピンが3以上の零質量の場が結合した系を記述する理論である。
      このような理論は非常に曲がった空間上の弦理論の有効理論であることが期待され、非常に注目を集めている。4次元以上ではその運動方程式は大変複雑であるが、3次元ではある種のChern Simons理論により記述することができ、取り扱いが容易である。
      このような理論におけるブラックホール解(higher spinブラックホール)を研究することで、弦理論におけるブラックホールをよりよく理解できることが期待される。3次元におけるHigher spinブラックホール解はいくつか発見されているが、今までそのエントロピーを計算する公式は知られていなかった。私はhigher spinブラックホールのエントロピー公式を発見し、それが正しい熱力学第一法則を満たすことを発見した。ところでhigher spinブラックホールの因果構造についてはその定義も含めてよくわかっていない。この間題を解決するために、ブラックホールの事象の地平面の内側の情報を反映する、量子クエンチにおけるエンタングルメントエントロピーの時間発展を議論した。特に一般的な量子クエンチに対応する時空を構成する方法を提案し、その時空における極小曲面の面積からエンタングルメントエントロピーの時間発展が計算できることを示した。

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