2023/03/22 更新

写真a

ミヤシタ ショウイチロウ
宮下 翔一郎
Scopus 論文情報  
論文数: 8  Citation: 21  h-index: 3

Click to view the Scopus page. The data was downloaded from Scopus API in March 21, 2023, via http://api.elsevier.com and http://www.scopus.com .

所属
理工学術院 先進理工学部
職名
講師(任期付)

経歴

  • 2020年04月
    -
    継続中

    早稲田大学   先進理工学部 応用物理学科   講師

学歴

  • 2017年04月
    -
    2020年03月

    早稲田大学   大学院先進理工学研究科   物理学及応用物理学専攻  

  • 2015年04月
    -
    2017年03月

    早稲田大学   大学院先進理工学研究科   物理学及応用物理学専攻  

  • 2011年04月
    -
    2015年03月

    早稲田大学   先進理工学部   応用物理学科  

所属学協会

  • 2015年09月
    -
    継続中

    日本物理学会

研究分野

  • 素粒子、原子核、宇宙線、宇宙物理にする理論   一般相対性理論

研究キーワード

  • AdS/CFT対応

  • ホログラフィ原理

  • ブラックホール

  • 一般相対性理論

  • 重力

 

論文

  • Rotating particles in AdS: Holography at weak gauge coupling and without conformal symmetry

    Tomotaka Kitamura, Shoichiro Miyashita, Yasuhiro Sekino

    Progress of Theoretical and Experimental Physics   2022 ( 4 )  2022年04月

     概要を見る

    Abstract

    We consider the gauge/gravity correspondence between maximally supersymmetric Yang–Mills theory in (p + 1) dimensions and superstring theory on the near-horizon limit of the Dp-brane solution. The string-frame metric is AdSp + 2 × S8 − p times a Weyl factor, and there is no conformal symmetry except for p = 3. In a previous paper by one of the present authors, the free-field result of gauge theory has been reproduced from string theory for a particular operator that has angular momentum along S8 − p. In this paper, we extend this result to operators that have angular momenta along AdSp + 2. Our approach is based on a Euclidean formulation proposed by Dobashi et al. [Nucl. Phys. B 665, 94 (2003)] and on the “string bit” picture. We first show that the spinning string solution in Lorentzian AdS, found by Gubser et al. [Nucl. Phys. B 636, 99 (2002)], can be recast in a form that connects two points on the boundary of Euclidean AdS. The transition amplitudes of such strings can be interpreted as gauge theory correlators. We study the case of zero gauge coupling by ignoring interactions among string bits (massless particles in 10D spacetime that constitute a string), and show that the free-field results of gauge theory are reproduced.

    DOI

    Scopus

  • Gravitational and gravitoscalar thermodynamics

    Shoichiro Miyashita

    Journal of High Energy Physics   2021 ( 9 )  2021年09月

     概要を見る

    Abstract

    Gravitational thermodynamics and gravitoscalar thermodynamics with S2 × ℝ boundary geometry are investigated through the partition function, assuming that all Euclidean saddle point geometries contribute to the path integral and dominant ones are in the B3 × S1 or S2 × Disc topology sector. In the first part, I concentrate on the purely gravitational case with or without a cosmological constant and show there exists a new type of saddle point geometry, which I call the “bag of gold(BG) instanton,” only for the Λ > 0 case. Because of this existence, thermodynamical stability of the system and the entropy bound are absent for Λ > 0, these being universal properties for Λ ≤ 0. In the second part, I investigate the thermodynamical properties of a gravity-scalar system with a φ2 potential. I show that when Λ ≤ 0 and the boundary value of scalar field Jφ is below some value, then the entropy bound and thermodynamical stability do exist. When either condition on the parameters does not hold, however, thermodynamical stability is (partially) broken. The properties of the system and the relation between BG instantons and the breakdown are discussed in detail.

    DOI

  • Role of Mann Counterterm in Gravitational Energy

    Shoichiro Miyashita

       2020年07月

     概要を見る

    In 1999, R. B. Mann proposed a counterterm that is some sort of
    generalization of the well-known Holographic counterterm and that can eliminate
    the divergence of the gravitational action of asymptotically AdS and flat
    spacetimes (Phys. Rev. D $\boldsymbol{60}$ (1999) 104047 [1]). I show it is not
    only for eliminating the divergence of such spacetimes but also for setting the
    ground state energy to zero for any $d$-dimensional spacetimes with an $S^{d-2}
    \times \mathbb{R} $ boundary geometry, and speculate it is also true for
    spacetimes with any (suitable) boundary geometry and topology.

  • 熱平衡状態に於ける重力の量子論的側面

    宮下 翔一郎

       2020年03月

  • Energy spectrum of a quantum spacetime with boundary

    Shoichiro Miyashita

    Classical and Quantum Gravity   36 ( 15 ) 155003 - 155003  2019年08月

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Stable Singularity-free Cosmological Solutions in non-projectable Horava-Lifshitz Gravity

    Mitsuhiro Fukushima, Yosuke Misonoh, Shoichiro Miyashita, Seiga Sato

    PHYSICAL REVIEW D   99 ( 6 )  2018年12月

     概要を見る

    We find stable singularity-free cosmological solutions in non-flat
    Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) spacetime in the context of
    Ho\v{r}ava-Lifshitz (HL) theory. Although we encounter the negative squared
    effective masses of the scalar perturbations in the original HL theory, the
    behaviors can be remedied by relaxing the projectability condition. In our
    analysis, the effects from the background dynamics are taken into account as
    well as the sign of the coefficients in the quadratic action for perturbations.
    More specifically, we give further classification of the gradient
    stability/instability into five types. These types are defined in terms of the
    effective squared masses of perturbations $\mathcal{M}^2$, the effective
    friction coefficients in perturbation equations $\mathcal{H}$ and these
    magnitude relations $|\mathcal{M}^2|/\mathcal{H}^2$. Furthermore, we indicate
    that oscillating solutions possibly show a kind of resonance especially in open
    FLRW spacetime. We find that the higher order spatial curvature terms with
    Lifshitz scaling $z=3$ are significant to suppress the instabilities due to the
    background dynamics.

    DOI

    Scopus

    6
    被引用数
    (Scopus)
  • Stability of Singularity-free Cosmological Solutions in Hořava-Lifshitz Gravity

    Yosuke Misonoh, Mitsuhiro Fukushima, Shoichiro Miyashita

    PHYSICAL REVIEW D   95 ( 4 )  2016年12月

     概要を見る

    We study stability of singularity-free cosmological solutions with positive
    cosmological constant based on projectable Ho\v{r}ava-Lifshitz (HL) theory. In
    HL theory, the isotropic and homogeneous cosmological solutions with bounce can
    be realized if spacial curvature is non-zero. By performing perturbation
    analysis around non-flat Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime,
    we derive a quadratic action and discuss the stability, i.e, ghost and
    tachyon-free conditions. Although the squared effective mass of scalar
    perturbation must be negative in infrared regime, we can avoid tachyon
    instability by considering strong Hubble friction. Additionally, we estimate
    the backreaction from the perturbations on background geometry, especially,
    against anisotropic perturbation in closed FLRW spacetime. It turns out that
    certain types of bouncing solution may be spoiled even if all perturbation
    modes are stable.

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • AdS monopole black hole and phase transition

    Shoichiro Miyashita, Kei-ichi Maeda

    Physical Review D   94 ( 12 )  2016年12月

    DOI

▼全件表示

 

特定課題制度(学内資金)

  • 量子重力の粗視化された性質の探求

    2021年  

     概要を見る

    重力の量子論については未だ完全な定式化は存在せず、重力系の量子力学的ダイナミクスを追うことは現時点では出来ていない。しかしながらある程度粗視化されたダイナミクスについては統計力学の手法によって理解できるということが知られている。本研究では昨年度に引き続きその手法を用いて正の宇宙項の場合や物質と結合している場合の(熱)平衡状態について考察した。特に、電磁場と結合した場合についても調べ、Hawking-Page相転移が起こることを示した。

  • 重力の量子化とホログラフィー

    2020年  

     概要を見る

    重力の量子論については未だ完全な定式化は存在せず、重力系の量子力学的ダイナミクスを追うことは現時点では出来ていない。しかしながらある程度粗視化されたダイナミクスについては統計力学の手法によって理解できるということが知られている。本研究ではその手法を用いて正の宇宙項の場合や物質と結合している場合の(熱)平衡状態について考察した。また、重力の経路積分を定義する際に必要な相殺項として普遍的なものはこれまで知られておらず、状況に応じてその都度適当なものを設定する必要があったが、本研究では普遍的な相殺項の候補を提唱した。