Updated on 2025/10/22

写真a

 
YOSHIDA Daisuke
 
Organization
Graduate School of Mathematics Division of Mathematics Designated Assistant Professor
Title
Designated Assistant Professor

Degree 1

  1. 博士（理学） （ 2017.3   東京工業大学 ） 

To the head of Degree.▲
 

Papers 8

  1. Multi-sheet wormholes in the gravitational soliton formalism Reviewed

    Makita, Y; Izumi, K; Yoshida, D; Uemichi, K

    CLASSICAL AND QUANTUM GRAVITY   Vol. 42 ( 17 )   2025.9

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    Language：English   Publishing type：Research paper (scientific journal)   Publisher：Classical and Quantum Gravity  

    We analytically construct static regular solutions describing wormholes that connect multiple asymptotic regions, supported by a phantom scalar field. The solutions are static and axially symmetric, and are constructed using the gravitational soliton formalism, in which the equations of motion reduce to the Laplace equations on a two-dimensional sheet. However, the presence of multiple asymptotic regions necessitates the introduction of multiple such sheets. These sheets are appropriately cut and glued together to form a globally regular geometry. This gluing procedure represents the principal distinction from conventional Weyl-type solitonic solutions and is a characteristic feature of the wormhole geometries studied in this paper.

    DOI： 10.1088/1361-6382/adfeb0

    Web of Science

    Scopus

  2. The first law and weak cosmic censorship for de Sitter black holes Reviewed

    Yoshida, D; Yoshimura, K

    CLASSICAL AND QUANTUM GRAVITY   Vol. 42 ( 11 )   2025.6

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    Language：English   Publishing type：Research paper (scientific journal)   Publisher：Classical and Quantum Gravity  

    We apply Iyer-Wald’s covariant phase space formalism to asymptotically de Sitter spacetimes and establish the thermodynamic first law, expressed in terms of the Abbott-Deser mass. Similar to Iyer-Wald’s first law for asymptotically flat black holes, our first law applies to general asymptotically de Sitter perturbations around a Reissner-Nordström-de Sitter black hole, without imposing any symmetry for the perturbations. We explicitly derive the first law up to the second order in perturbation. Additionally, we apply this first law to a thought experiment involving the overcharging of a Reissner-Nordström-de Sitter black hole by injecting energy and charge sources. We find that asymptotically de Sitter black holes cannot be overcharged, provided that the null energy condition holds, thereby reinforcing the weak cosmic censorship conjecture.

    DOI： 10.1088/1361-6382/add787

    Web of Science

    Scopus

  3. Removing naked singularities in static axially symmetric spacetimes by patching with flat spacetimes Reviewed

    Saito, D; Yoshida, D

    PHYSICAL REVIEW D   Vol. 111 ( 2 )   2025.1

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    Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Review D  

    We investigate static, axially symmetric spacetimes without naked singularities that are constructed by patching Weyl class spacetimes with the flat spacetimes. Once the exterior geometry is specified, the junction conditions determine the shape of a thin shell, which is the boundary between the two patched spacetimes, and the distribution of the energy and pressure on this shell, leaving a parameter representing the shell size free. We examine the cases where the exterior of the shell is given by Curzon-Chazy or Zipoy-Voorhees spacetimes. For each case, we find a lower bound on the shell size. Additionally, we find that the weak and null energy conditions are satisfied for any shell size, while the dominant energy condition is satisfied for sufficiently large shells. These results provide concrete examples of nonsingular spacetimes with nonspherically symmetric exteriors that respect the energy conditions.

    DOI： 10.1103/PhysRevD.111.024031

    Web of Science

    Scopus

  4. Loosely Trapped Surface for Slowly Rotating Black Hole Reviewed Open Access

    Izumi, K; Shiromizu, T; Yoshida, D; Tomikawa, Y; Yoshino, H

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   Vol. 2024 ( 11 )   2024.11

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    Language：English   Publishing type：Research paper (scientific journal)   Publisher：Progress of Theoretical and Experimental Physics  

    We construct the marginal loosely trapped surface (marginal LTS) for the Kerr spacetime with a small Kerr parameter perturbatively, where the LTS condition is saturated. An LTS is a surface that specifies the strong gravity region, which is a generalization of the photon sphere in the Schwarzschild spacetime. It turns out that there are an infinite number of marginal LTSs. At the leading order of the small Kerr parameter, all of the marginal LTSs have the same area. However, one can see that the maximal marginal LTS among them is uniquely determined at the higher order.

    DOI： 10.1093/ptep/ptae158

    Open Access

    Web of Science

    Scopus

  5. Cutoff scale of quadratic gravity from quantum focusing conjecture Reviewed Open Access

    Kanai, T; Maeda, K; Noumi, T; Yoshida, D

    PHYSICAL REVIEW D   Vol. 110 ( 8 )   2024.10

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    Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Review D  

    We derive the cutoff length scale of the quadratic gravity in d≥5 dimensional spacetime by demanding that the quantum focusing conjecture for the smeared quantum expansion holds at the classical level. The cutoff scale has a different dependence on the spacetime dimension depending on the sign of the coupling constant of the quadratic gravity. We also investigate a concrete example of the five-dimensional Schwarzschild spacetime and directly confirm that the quantum focusing conjecture holds when the quantum expansion is smeared over the scale larger than our cutoff scale.

    DOI： 10.1103/PhysRevD.110.084037

    Open Access

    Web of Science

    Scopus

  6. Gedanken experiments to destroy a black hole by a test particle: Multiply charged black hole with higher derivative corrections Reviewed Open Access

    Izumi, K; Noumi, T; Yoshida, D

    PHYSICAL REVIEW D   Vol. 110 ( 4 )   2024.8

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    Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Review D  

    We investigate a gedanken experiment to destroy an extremally charged black hole by dropping a test particle, provided that there are multiple U(1) gauge fields coupled with each other through higher derivative interactions. It is known that the Coulomb repulsion prevents a test particle that would break the extremal condition from falling into an extremal black hole and therefore the black hole cannot be destroyed. We extend this observation to include higher derivative corrections. Although the extremal condition is modified by the higher derivative interactions, we find that the repulsive force induced by the higher derivative couplings is responsible for preventing a test particle that would break the modified extremal condition to reach the event horizon. Thus, we confirm that the weak cosmic censorship conjecture holds for extremally charged black holes even in the presence of higher derivative corrections, as long as the test particle approximation is justified.

    DOI： 10.1103/PhysRevD.110.044008

    Open Access

    Web of Science

    Scopus

  7. Entropy bound and a geometrically nonsingular universe Reviewed

    Kanai, T; Nomura, K; Yoshida, D

    PHYSICAL REVIEW D   Vol. 108 ( 10 )   2023.11

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    Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Review D  

    Bousso's entropy bound is a conjecture that the entropy through a null hypersurface emanating from a two-dimensional surface with a nonpositive expansion is bounded by the area of that two-dimensional surface. We investigate the validity of Bousso's entropy bound in the spatially flat, homogeneous, and isotropic universe with an adiabatic entropy current. We find that the bound is satisfied in the entire spacetime in which a cutoff time is introduced based on the entropy density and the energy density. Compared to the previously used prescription which puts a cutoff near the curvature singularity, our criterion for introducing the cutoff is applicable even to a nonsingular universe. Our analysis provides an interpretation of the incompleteness implied by the recently proposed singularity theorem based on the entropy bounds.

    DOI： 10.1103/PhysRevD.108.104024

    Web of Science

    Scopus

  8. Implications of the singularity theorem for the size of a nonsingular universe Reviewed International journal Open Access

    Nomura, K; Yoshida, D

    PHYSICAL REVIEW D   Vol. 106 ( 12 )   2022.12

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    Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Review D  

    A general property of universes without initial singularity is investigated based on the singularity theorem, assuming the null convergence condition and the global hyperbolicity. As a direct consequence of the singularity theorem, the universal covering of a Cauchy surface of a nonsingular universe with a past trapped surface must have the topology of S3. In addition, we find that the affine size of a nonsingular universe, defined through the affine length of null geodesics, is bounded above. In the case where a part of the nonsingular spacetime is described by Friedmann-Lemaître-Robertson-Walker spacetime, we find that this upper bound can be understood as the affine size of the corresponding closed de Sitter universe. We also evaluate the upper bound of the affine size of our Universe based on the trapped surface confirmed by recent observations of baryon acoustic oscillations, assuming that our Universe has no initial singularity.

    DOI： 10.1103/PhysRevD.106.124016

    Web of Science

    Scopus

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To the head of Papers.▲

Presentations 28

  1. 漸近的反ドジッター時空におけるバルクショートカットについて

    吉田大介

    日本物理学会第80回年次大会(2025)  2025.9.16 

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    Event date： 2025.9

    Language：Japanese   Presentation type：Oral presentation (general)  

    Country：Japan  

  2. Apparent Horizons Associated with Dynamical Black Hole Entropy

    Daisuke Yoshida

    QG Summer Workshop 2025  2025.9.12 

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    Event date： 2025.9

    Language：English   Presentation type：Oral presentation (general)  

    Country：Japan  

  3. Wormholes as Perturbations of Near-Horizon, Near-Extremal Black Hole Geometries: No-Go Theorems

    2025.9.5 

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    Event date： 2025.9

    Language：English   Presentation type：Oral presentation (general)  

    Country：Japan  

  4. Introduction to the Causal Structure of Spacetime Invited International conference

    Daisuke Yoshida

    The 7th "Extreme Universe" School  2025.6.30 

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    Event date： 2025.6 - 2025.7

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

    Country：Japan  

  5. Removing naked singularities in static axially symmetric spacetimes by patching with the flat spacetimes International conference

    Daisuke Yoshida

    Gravity 2025: New Horizon of Black Hole Physics  2025.1.27 

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    Event date： 2025.1

    Language：English   Presentation type：Oral presentation (general)  

    Country：Japan  

  6. The First Law and Cosmic Censorship for de Sitter Black Holes International conference

    Daisuke Yoshida

    2nd Bangkok workshop on Gravity & Cosmology  2025.1.10 

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    Event date： 2025.1

    Language：English   Presentation type：Oral presentation (general)  

    Country：Thailand  

  7. Can Charged Shells Extremize or Overcharge Black Holes? International conference

    Daisuke Yoshida

    The 33rd Workshop on General Relativity and Gravitaion in Japan  2024.12.2 

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    Event date： 2024.12

    Language：English   Presentation type：Oral presentation (general)  

    Country：Japan  

  8. First Law and Weak Cosmic Censorship for de Sitter Black Holes International conference

    Daisuke Yoshida

    Quantum Extreme Universe: Matter, Information, and Gravity  2024.10.21 

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    Event date： 2024.10

    Language：English   Presentation type：Poster presentation  

    Country：Japan  

  9. First Law and Weak Cosmic Censorship for de Sitter Black Holes

    Daisuke Yoshida

    Fourth Annual Meeting of Extreme Universe Collaboration  2024.9.27 

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    Event date： 2024.9

    Language：English   Presentation type：Poster presentation  

    Country：Japan  

  10. Thermodynamics of de Sitter black holes

    Daisuke Yoshida

    The 3rd young researchers‘ workshop of the Extreme Universe Collaboration  2024.9.14 

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    Event date： 2024.9

    Language：English   Presentation type：Oral presentation (invited, special)  

  11. ドジッター時空における ブラックホールの熱力学法則と宇宙検閲官仮説

    吉田大介

    第25回特異点研究会  2024.9.5 

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    Event date： 2024.9

    Language：Japanese   Presentation type：Oral presentation (general)  

  12. Thermodynamics of de Sitter black holes and the cosmic censorship conjecture

    Daisuke Yoshida

    QG Summer Workshop 2024  2024.8.30 

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    Event date： 2024.8

    Language：English   Presentation type：Oral presentation (general)  

  13. Initial Singularities of the Universe Invited International conference

    Daisuke Yoshida

    From Fundamental Physics to the Universe  2024.3.2 

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    Event date： 2024.3

    Language：English   Presentation type：Oral presentation (invited, special)  

    Country：India  

  14. Singularity Theorem & Initial Singularity of the Universe

    Daisuke Yoshida

    The second young researchers' workshop of the Extreme Universe Collaboration  2024.2.20 

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    Event date： 2024.2

    Language：English   Presentation type：Oral presentation (general)  

  15. 特異点の無い宇宙の大きさについて

    吉田大介

    2024.2.11 

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    Event date： 2024.2

    Language：Japanese   Presentation type：Oral presentation (general)  

  16. 特異点の無い宇宙の大きさについて

    吉田大介

    一般相対論と幾何  2024.2.8 

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    Event date： 2024.2

    Language：Japanese   Presentation type：Oral presentation (general)  

  17. Entropy Bound and Geometrically Nonsingular Universe

    Cosmology and Gravity at Kobe 2023  2023.9.29 

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    Event date： 2023.9

    Language：Japanese   Presentation type：Oral presentation (general)  

  18. ゲージ場間の相互作用と裸の特異点について

    吉田大介

    日本物理学会第78回年次大会(2023)  2023.9.16 

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    Event date： 2023.9

    Language：Japanese   Presentation type：Oral presentation (general)  

  19. Entropy Bound and a Geometrically Nonsingular Universe International conference

    Daisuke Yoshida

    YIPQS long-term workshop Quantum Information, Quantum Matter and Quantum Gravity  2023.9.4 

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    Event date： 2023.9 - 2023.10

    Language：English   Presentation type：Oral presentation (general)  

    Country：Japan  

  20. ゲージ場間の相互作用と裸の特異点について

    吉田大介

    第24回特異点研究会  2023.8.31 

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    Event date： 2023.8 - 2023.9

    Language：Japanese   Presentation type：Oral presentation (general)  

  21. cosmic censorship conjecture and interaction between gauge fields International conference

    Daisuke Yoshida

    Gravity 2023: Dawn of field theoretic approach  2023.7.19 

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    Event date： 2023.7

    Language：English   Presentation type：Oral presentation (general)  

    Country：Japan  

  22. Entropy Bound and Non-Singular Universe

    Daisuke Yoshida

    The first young researchers' workshop of the Extreme Universe Collaboration  2023.2.16 

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    Event date： 2023.2

    Language：English   Presentation type：Poster presentation  

  23. Entropy Bound and Non-singular universe

    2022.12.30 

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    Event date： 2022.12

    Language：Japanese   Presentation type：Oral presentation (general)  

  24. Implications of the Singularity Theorem for the Size of a Non-Singular Universe

    Daisuke Yoshida

    Second Annual Meeting of Extreme Universe Collaboration  2022.12.27 

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    Event date： 2022.12

    Language：English   Presentation type：Poster presentation  

  25. 特異点の無い宇宙の一般的性質について

    吉田大介

    日本物理学会2022年秋季大会  2022.9.7 

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    Event date： 2022.9

    Language：Japanese   Presentation type：Oral presentation (general)  

  26. Implications of the singularity theorem for the size of a non-singular universe

    Daisuke Yoshida

    QG summer school 2022  2022.9.1 

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    Event date： 2022.8 - 2022.9

    Language：English   Presentation type：Oral presentation (general)  

  27. Kobe Workshop on Cosmology and Fundamental Physics Invited International conference

    Daisuke Yoshida

    Implications of the singularity theorem for the size of a non-singular universe  2022.7.7 

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    Event date： 2022.7

    Language：English   Presentation type：Oral presentation (invited, special)  

    Country：Japan  

  28. Implications of singularity theorem for non-singular universe

    Daisuke Yoshida

    Gravity: Current challenges in black hole physics and cosmology  2022.6.24 

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    Event date： 2022.6 - 2022.7

    Language：English   Presentation type：Oral presentation (general)  

    Country：Japan  

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To the head of Presentations.▲

KAKENHI (Grants-in-Aid for Scientific Research) 1

  1. 量子重力理論に基づくインフレーション以前の宇宙像

    Grant number：20K14469  2020.4 - 2025.3

    科学研究費助成事業  若手研究

    吉田 大介

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    Authorship：Principal investigator 

    Grant amount：\4160000 （ Direct Cost: \3200000 、 Indirect Cost：\960000 ）

    現在の標準的な宇宙論では、宇宙はビックバン期以前にインフレーション期にあったとされています。このようなインフレーション宇宙は過去に遡っていくと初期特異点に到達する場合が知られています。本研究では、量子宇宙論と超弦理論の2種の量子重力理論に基づき、特異点を解消したインフレーション以前の宇宙像を明らかにすることを目的とします。量子宇宙論については、近年提唱された特異点の無い振動宇宙からインフレーション宇宙へのトンネル効果による遷移モデルの不安定性の問題の解決に臨みます。超弦理論については、インフレーション宇宙の初期特異点の、弦の巻き付き自由度による解消機構を定式化を行います。
    本研究は、時空特異点の無いようなインフレーション以前の宇宙像の解明を目標としています。前年度の研究では、ヌルエネルギー条件に基づくペンローズの特異点定理を応用し、特異点の無い宇宙の普遍的性質を解明しました。そこでは、宇宙がヌルエネルギー条件を満たしていたとしても、宇宙空間がコンパクトでかつ、ヌル測地線に基づく宇宙の大きさが、膨張率で決まる上限より小さい場合には、特異点の無い宇宙が得られる、ということが明らかになりました。
    近年、エントロピーの議論に基づく新しい視点による特異点定理が提唱されています。ペンローズの特異点定理と比較すると、コンパクトな空間を持った時空に対しても、特異点の存在を予言するという点が大きな違いです。本年度は、このようなエントロピーに基づく特異点定理と、従来のペンローズの特異点定理の相違について研究を行いました。特に、ペンローズの定理の仮定を破るコンパクトな空間を持った特異点の無い宇宙に対し、エントロピーの性質を調べました。その結果、このような例では、エントロピー密度に対する特異点が生じており、エントロピーに基づく特異点定理の仮定が破れていることを明らかにしました。
    昨年度に引き続き、特異点定理の立場から特異点の無い宇宙の新たな性質を調べることができました。特に、エントロピーという新しい視点から理解が得られたため、研究はおおむね順調に進展していると判断できます。
    本年度の研究で扱ったようなエントロピーと時空の特異点の性質をより深く理解していきたいと考えています。特に、エントロピーの性質と、特異点定理の鍵となる時空に対するヌルエネルギー条件の両者を包括する形での一般化として提唱されている、量子的ヌルエネルギー条件に注目し、高階微分重力理論を用いた検証を行おうと計画しています。

To the head of KAKENHI (Grants-in-Aid for Scientific Research).▲