arXiv subjects

Shoichiro Miyashita

Publications and source records attributed to Shoichiro Miyashita.

14 recordsLinked to original sources

arXiv2026

The mini-Page Curve in Cosmology

The black hole information paradox has motivated extensive study of how and when information escapes from evaporating black holes. Here we address the analogous question for cosmological horizons: when does an individual Hawking pair begin to carry information out of a de Sitter horizon? We study this problem in a class of two-dimensional flow geometries that interpolate smoothly between an asymptotic AdS$ _2 $ boundary and a dS$ _2 $ static patch. Modeling the emission of a Hawking pair via a probe state constructed from local operators and their modular conjugates, we promote the centaur algebra of observables to a Type II$ _\infty $ factor through the crossed-product construction. This allows us to compute the entropy difference between the thermofield-double reference state and the Hawking-pair state. We find that this difference traces a characteristic mini-Page curve for the cosmological horizon: it starts near zero, reaches a minimum near $ τ\approx β/8 $ before increasing again. We interpret the location of the minimum as the time at which quantum information begins to escape the cosmological horizon. Extending the analysis to the microcanonical ensemble, we show that the algebraic entropy coincides with the generalized entropy of an entanglement wedge cut that tracks the emitted particle along the horizon. Furthermore, the relative modular flow generated between the two states yields a Lyapunov exponent $λ=2π/β$, identifying the scrambling time as the scale at which the information carried by the pair becomes accessible to a static-patch observer.

hep-th↗

arXiv2026

Holograms and Standard Models

Despite riddles, mysteries, and enigmas the theory of elementary particles has not changed for 50 years. We argue that the current paradigm -- Wilsonian quantum field theory -- is inadequate for resolving the puzzles, and should be replaced by a new paradigm based on the Holographic Principle. We show how a simplified but still very rich standard model emerges from de Sitter holography in the flat-space limit and explain why the puzzle of huge quantum corrections to the cosmological constant simply does not occur in the holographic paradigm.

hep-th↗

arXiv2026

Flow-geometry microstates

We construct geometric microstates for a class of two-dimensional flow geometries$-$spacetimes that interpolate from an asymptotic AdS$_2$ boundary to a dS$_2$ static patch in the interior$-$by inserting particles behind the horizon. We show that this mechanism produces dS microstates with an Einstein-Rosen bridge of infinite length behind the horizon. The state-counting of these microstates, including wormhole contributions, reproduces the Gibbons-Hawking entropy, $S_{\rm dS}=A^{\rm dS}_{\rm horizon}/4G$. Furthermore, we extend the microstate-counting method to the case of a finite-length Einstein-Rosen bridge. As a result, the Hilbert space of the dS horizon in the flow geometry can be spanned by states with a purely dS Einstein-Rosen bridge, containing no AdS portion on the time-symmetric slice. This provides a concrete realization of dS microstates within a controlled holographic framework.

hep-th↗

arXiv2025

DSSYK at Infinite Temperature: The Flat-Space Limit and the 't Hooft Model

In the limit of infinite radius de Sitter space becomes locally flat and the static patch tends to Rindler space. A holographic description of the static patch must result in a holographic description of some flat space theory, expressed in Rindler coordinates. Given such a holographic theory how does one decode the hologram and determine the bulk flat space theory, its particle spectrum, forces, and bulk quantum fields? In this paper we will answer this question for a particular case: DSSYK at infinite temperature and show that the bulk theory is a strongly coupled version of the 't Hooft model, i.e., (1+1)-dimensional QCD, with a single quark flavor. It may also be thought of as an open string theory with mesons lying on a single Regge trajectory.

hep-th↗

arXiv2025

Many phases in a hairy box in three dimensions

In this paper, I investigate gravitational thermodynamics of the Einstein-Maxwell-scalar system in three dimensions without a cosmological constant. In the previous work by Krishnan,Shekhar, and Bala Subramanian (Nucl. Phys. B 958 (2020) 115115 [33]), it was argued that this system has no BH saddles, but has only empty (flat space) saddles and boson star saddles. It was then concluded that the structure of the thermodynamic phase space is much simpler than in the higher dimensional cases. I will show that, in addition to the known boson star and empty saddles, three more types of saddles exist in this system: the BG saddle, its hairy generalization, and a novel configuration called the boson star-PL saddle. As a result, the structure is richer than one might naively expect and is very similar to the higher dimensional ones.

gr-qc↗

arXiv2024

Thermodynamics of the 3-dimensional Einstein-Maxwell system

Recently, I studied the thermodynamical properties of the Einstein-Maxwell system with a box boundary in 4-dimensions [1](JHEP 04 (2024) 083). In this paper, I investigate those in 3-dimensions using the zero-loop saddle-point approximation and focusing only on a simple topology sector as usual. Similar to the 4-dimensional case, the system is thermodynamically well-behaved when $Λ<0$ (due to the contribution of the "bag of gold" saddles). However, when $Λ=0$, a crucial difference to the 4-dimensional case appears, i.e. the 3-dimensional system turns out to be thermodynamically unstable, while the 4-dimensional one is thermodynamically stable. This may offer two options for how we think about the thermodynamics of 3-dimensional gravity with $Λ=0$. One is that the zero-loop approximation or restricting the simple topology sector is not sufficient for 3-dimensions with $Λ=0$. The other is that 3-dimensional gravity is really thermodynamically unstable when $Λ=0$.

gr-qc↗

arXiv2024

Thermodynamics of the Einstein-Maxwell system

At first glance, thermodynamic properties of gravity with asymptotically AdS conditions and those with box boundary conditions, where the spatial section of the boundary is a sphere of finite radius, appear similar. Both exhibit a similar phase structure and Hawking-Page phase transition. However, when we introduce a U(1) gauge field to the system, discrepancies in thermodynamic properties between the two cases has been reported in [7] (JHEP 11 (2016) 041). In this paper, by accepting the assumption that all Euclidean saddles contribute to the partition function, I found that these discrepancies are resolved due to the contribution from the "bag of gold (BG)," which is the class of Euclidean geometries whose area of bolt is bigger than that of the boundary. As a result, the Hawking-Page phase structure is restored, with the unexpected properties that the upper bound of thermodynamic entropy is always larger than the boundary area divided by 4G when the chemical potential is non-zero, and that such high entropy states are realized at sufficiently high temperature.

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arXiv2022

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

We consider gauge/gravity correspondence between maximally supersymmetric Yang-Mills theory in ($p+1$) dimensions and superstring theory on the near-horizon limit of the D$p$-brane solution. The string-frame metric is AdS$_{p+1}\times S^{8-p}$ 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 which has angular momentum along $S^{8-p}$. In this paper, we extend this result to operators which have angular momenta along AdS$_{p+2}$. Our approach is based on a Euclidean formulation proposed by Dobashi, Shimada and Yoneya and on the "string bit" picture. We first show that the spinning string solution in Lorentzian AdS, found by Gubser, Klebanov and Polyakov, can be recast in a form which connects two points on the boundary of Euclidean AdS. 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 ten-dimensional spacetime which constitute a string), and show that the free-field results of gauge theory are reproduced.

hep-th↗

arXiv2021

Gravitational and Gravitoscalar Thermodynamics

Gravitational thermodynamics and gravitoscalar thermodynamics with $S^2 \times \mathbb{R}$ 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 $B^3 \times S^1$ or $S^2 \times Disc$ 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 $Λ\leq 0$. In the second part, I investigate the thermodynamical properties of a gravity-scalar system with a $φ^2$ potential. I show that when $Λ\leq 0$ and the boundary value of scalar field $J_φ$ 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.

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arXiv2020

Role of Mann Counterterm in Gravitational Energy

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.

gr-qc↗

arXiv2019

Energy spectrum of a quantum spacetime with boundary

In this paper, I revisit the microcanonical partition function, or density of states (DOS), of general relativity. By using the minisuperspace path integral approximation, I directly calculate the $S^2 \times Disc$ topology sector of the DOS of a (quantum) spacetime with an $S^2\times \mathbb{R}$ Lorentzian boundary from the microcanonical path integral, in contrast with previous works in which DOSs are derived by inverse Laplace transformation from various canonical partition functions. Although I found there always exists only one saddle point for any given boundary data, it does not always dominate the possible integration contours. There is another contribution to the path integral other than the saddle point. One of the obtained DOSs has behavior similar to that of the previous DOSs; that is, it exhibits exponential Bekenstein--Hawking entropy for the limited energy range $ (1-\sqrt{2/3}) <GE/R_{b}< (1+\sqrt{2/3})$, where energy $E$ is defined by the Brown--York quasi-local energy momentum tensor and $R_{b}$ is the radius of the boundary $S^2$. In that range, the DOS is dominated by the saddle point. However, for sufficiently high energy, where the saddle point no longer dominates, the DOS approaches a positive constant, different from the previous ones, which approach zero.

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arXiv2019

Stable Singularity-free Cosmological Solutions in non-projectable Horava-Lifshitz Gravity

We find stable singularity-free cosmological solutions in non-flat Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime in the context of Hořava-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.

gr-qc↗

arXiv2017

Stability of Singularity-free Cosmological Solutions in Hořava-Lifshitz Gravity

We study stability of singularity-free cosmological solutions with positive cosmological constant based on projectable Hořava-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.

gr-qc↗

arXiv2016

AdS Monopole Black Hole and Phase Transition

We study the Einstein-SO(3)Yang-Mills-Higgs system with a negative cosmological constant, and find the monopole black hole solutions as well as the trivial Reissner-Nordström black hole. We discuss thermodynamical stability of the monopole black hole in an isolated system. We expect a phase transition between those two black holes when the mass of a black hole increases or decreases. The type of phase transition depends on the cosmological constant $Λ$ as well as the vacuum expectation value $v$ and the coupling constant $λ$ of the Higgs field. Fixing $λ$ small, we find there are two critical values of the cosmological constant $Λ_{\rm cr (1)}(v)$ and $Λ_{\rm cr(2)}(v)$, which depend on $v$. If $Λ_{\rm cr(1)}(v)<Λ(<0)$, we find the first order transition, while if $Λ_{\rm cr(2)}(v)<Λ<Λ_{\rm cr(1)}(v)$, the transition becomes second order. For the case of $Λ_{b}(v)<Λ<Λ_{\rm (2)}(v)$, we again find the first order irreversible transition from the monopole black hole to the extreme Reissner-Nordström black hole. Beyond $Λ_{b}(v)$, no monopole black hole exists. We also discuss thermodynamical properties of the monopole black hole in a thermal bath system.

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