arXiv subjects

Yoshinori Matsuo

Publications and source records attributed to Yoshinori Matsuo.

At least 19 recordsLinked to original sources

arXiv2026

Interior of Schwarzschild in semiclassical gravity

In Einstein gravity, matter with an arbitrarily small density can be a black hole. Pressure in the star diverges if size of the star is smaller than 9/8 of the Schwarzschild radius, implying the gravitational collapse into a black hole. By taking quantum effects of matter, however, pressure is bounded from above, and a core with negative energy appears instead. Density of matter increases and eventually reaches the cut-off scale as size of the star approaches the Schwarzschild radius. This result implies that density must be very large as the Planck scale if the star is put inside the Schwarzschild radius.

hep-th↗

arXiv2025

Self-gravitating strings and quantum effects in two-dimensional gravity

It is expected that when the string coupling is taken to be sufficiently small, a black hole turns into a bound state of self-gravitating fundamental strings. This state would be described by winding strings wrapping around the Euclidean time circle, known as the Horowitz-Polchinski solution. In this paper, we study such a self-gravitating string configuration in two-dimensional dilaton gravity theories. We first derive an analytic expression of the solution describing a winding string in two-dimensions and investigate in detail the geometry of this solution. Our winding string solution in two dimensions describes the geometry near the surface of the bound state of self-gravitating strings in the large-dimension limit, much like a two-dimensional black hole describes the near horizon geometry of the Schwarzschild black hole in the large-dimension limit. To study quantum effects around self-gravitating strings, we obtain an analytic solution of winding strings in the RST model. In a similar fashion to the Hartle-Hawking vacuum around a black hole, our string solution in the RST model contains the background radiation, whose temperature is the same as that of the winding strings.

hep-th↗

arXiv2024

Universal structure of islands in evaporating black holes

The entanglement entropy of the Hawking radiation contains contributions from a region inside the black hole, which is called islands, implying that the Hawking radiation contains the information of islands. The boundary of the island is given by the quantum extremal surface, whose position is determined so that the entanglement entropy is extremized. In many cases of stationary black holes and a few cases of evaporating black holes, it was already confirmed that the quantum extremal surface is located outside the horizon for stationary black holes and is inside the horizon for evaporating black holes. In this paper, we calculate islands in general black holes and show that the island extends to the outside of the horizon for stationary black holes but is hidden inside the horizon for evaporating black holes independent of details of the black hole.

hep-th↗

arXiv2024

Quantum focusing conjecture in two-dimensional evaporating black holes

We consider the quantum focusing conjecture (QFC) for two-dimensional evaporating black holes. The QFC is closely related to the behavior of the generalized entropy -- the sum of the area entropy for a given co-dimension two surface and the entanglement entropy for quantum fields outside the area. In the context of the black hole evaporation, the entanglement entropy of the Hawking radiation is decreasing after the Page time, and therefore it is not obvious whether the QFC holds in the black hole evaporation process especially after the Page time. One of the present authors previously addressed this problem in a four-dimensional spherically symmetric dynamical black hole model and showed that the QFC is satisfied. However the background spacetime considered was approximated by the Vaidya metric, and quantum effects of matters in the semiclassical regime is not fully taken into consideration. It remains to be seen if the QFC in fact holds for exact solutions of the semiclassical Einstein equations. In this paper, we address this problem in a two-dimensional dynamical black hole of the Russo-Susskind-Thorlacius (RST) model, which allows us to solve the semiclassical equations of motion exactly. We first give a suitable definition of the quantum expansion in two-dimensions and then prove that the QFC is satisfied for evaporating black holes in the RST model with the island formation taken into account.

hep-th↗

arXiv2023

Quantum focusing conjecture and the Page curve

The focusing theorem fails for evaporating black holes because the null energy condition is violated by quantum effects. The quantum focusing conjecture is proposed so that it is satisfied even if the null energy condition is violated. The conjecture states that the derivative of the sum of the area of a cross-section of the null geodesic congruence and the entanglement entropy of matters outside it is non-increasing. Naively, it is expected that the quantum focusing conjecture is violated after the Page time as both the area of the horizon and the entanglement entropy of the Hawking radiation are decreasing. We calculate the entanglement entropy after the Page time by using the island rule, and find the following results: (i) the page time is given by an approximately null surface, (ii) the entanglement entropy is increasing along the outgoing null geodesic even after the Page time, and (iii) the quantum focusing conjecture is not violated.

hep-th↗

arXiv2023

Fluid model of a black hole-string transition

A fluid model of self-gravitating strings is proposed. It is expected that black holes turn into strings around the end of black hole evaporation. The transition will occur near the Hagedorn temperature. After the transition, strings would form a bound state by the self-gravitation. Horowitz and Polchinski formulated a model of self-gravitating strings by using winding strings wrapping on the Euclidean time circle [arXiv:hep-th/9707170]. In this paper, we first show that winding strings in the Horowitz-Polchinski model approximately behave as a perfect fluid. Then, we solve the Einstein equation for the fluid of winding strings. Our solution reproduces behaviors of the self-gravitating string solution in the Horowitz-Polchinski model near the Hagedorn temperature, while it approaches the Schwarzschild black hole at low temperatures. Thus, our fluid model of self-gravitating strings gives a description of the transition between black holes and strings.

hep-th↗

arXiv2022

String is a double slit

We perform imaging of a fundamental string from string scattering amplitudes, and show that its image is a double slit.

hep-th↗

arXiv2022

Transient chaos analysis of string scattering

It has long been thought that a highly excited string can be regarded as a black hole: the correspondence principle between strings and a black hole, while recent studies found that black holes are characterized by chaos. This suggests that highly excited strings are the source of the black hole chaoticity. We study the chaoticity of a string amplitude where a tachyon is scattered by a highly excited string. Our strategy to extract the chaos in the amplitude is a generalization of the transient chaos analysis for classical scattering. We look for the fractal structure in the plots of incoming/outgoing scattering angles, where the outgoing angle is defined as the maximum pole of the amplitude. Within our strategy, we could not identify any fractal structure in the scattering data. We also discuss other possible setups and strategies to extract the chaos, hoping that our present work serves as a step toward the formulation of chaos in string scattering amplitudes.

hep-th↗

arXiv2022

Entanglement entropy and vacuum states in Schwarzschild geometry

Recently, it was proposed that there must be either large violation of the additivity conjecture or a set of disentangled states of the black hole in the AdS/CFT correspondence. In this paper, we study the additivity conjecture for quantum states of fields around the Schwarzschild black hole. In the eternal Schwarzschild spacetime, the entanglement entropy of the Hawking radiation is calculated assuming that the vacuum state is the Hartle-Hawking vacuum. In the additivity conjecture, we need to consider the state which gives minimal output entropy of a quantum channel. The Hartle-Hawking vacuum state does not give the minimal output entropy which is consistent with the additivity conjecture. We study the entanglement entropy in other static vacua and show that it is consistent with the additivity conjecture.

hep-th↗

arXiv2021

Distance between collapsing matter and trapping horizon in evaporating black holes

Assuming that the vacuum energy-momentum tensor is not exceptionally large, we consider 4D evaporating black holes with spherical symmetry and evaluate the proper distance $ΔL$ between the time-like apparent horizon and the surface of the collapsing matter after it has entered the apparent horizon. We show that $ΔL$ can never be larger than $\mathcal{O}(n^{3/2}\ell_p)$ when the black hole is evaporated to $1/n$ of its initial mass, as long as $n \ll a^{2/3}/\ell_p^{2/3}$ (where $a$ is the Schwarzschild radius and $\ell_p$ is the Planck length). For example, the distance between the matter and the apparent horizon must be Planckian at the Page time.

gr-qc↗

arXiv2021

Nuclear binding energy in holographic QCD

Saturation of the nuclear binding energy is one of the most important properties of atomic nuclei. We derive the saturation in holographic QCD, by building a shell-model-like mean-field nuclear potential from the nuclear density profile obtained in a holographic multi-baryon effective theory. The numerically estimated binding energy is close to the experimental value.

hep-th↗

arXiv2021

Islands and stretched horizon

Recently it was proposed that the entanglement entropy of the Hawking radiation contains the information of a region including the interior of the event horizon, which is called "island." In studies of the entanglement entropy of the Hawking radiation, the total system in the black hole geometry is separated into the Hawking radiation and black hole. In this paper, we study the entanglement entropy of the black hole in the asymptotically flat Schwarzschild spacetime. Consistency with the island rule for the Hawking radiation implies that the information of the black hole is located in a different region than the island. We found an instability of the island in the calculation of the entanglement entropy of the region outside a surface near the horizon. This implies that the region contains all information of the total system and the information of the black hole is localized on the surface. Thus the surface would be interpreted as the stretched horizon. This structure also resembles black holes in the AdS spacetime with an auxiliary flat spacetime, where the information of the black hole is localized at the interface between the AdS spacetime and the flat spacetime.

hep-th↗

arXiv2020

Islands in Schwarzschild black holes

We study the Page curve for asymptotically flat eternal Schwarzschild black holes in four and higher spacetime dimensions. Before the Page time, the entanglement entropy grows linearly in time. After the Page time, the entanglement entropy of a given region outside the black hole is largely modified by the emergence of an island, which extends to the outer vicinity of the event horizon. As a result, it remains a constant value which reproduces the Bekenstein-Hawking entropy, consistent with the finiteness of the von Neumann entropy for an eternal black hole.

hep-th↗

arXiv2020

Universal Higher-Order Topology from 5D Weyl semimetal: Edge topology, edge Hamiltonian and nested Wilson loop

Higher-order topological insulators (HOTIs) or multipole insulators, hosting peculiar corner states, were discovered [arXiv:1611.07987, arXiv:1708.03636]. It was independently discovered [arXiv:1702.00624] that continuum 5-dimensional (5D) Weyl semimetals generically host the corner states, and so do 4D class A and 3D class AIII topological insulators. In this paper we further confirm that the 5D Weyl semimetals, upon dimensional reduction, lead to universal higher-order topology. First we explain a discrete symmetry protecting the 5D Weyl semimetals, and describe dimensional reductions of the 5D Weyl semimetals to the popular HOTIs in the continuum limit. We calculate the topological charge carried by edge states of the 5D Weyl semimetal, for the most generic boundary condition. The topological charge is a Dirac monopole, which can also be seen from that edge Hamiltonians are always of the form of a 3D Weyl semimetal. This edge topology leads to the edge-of-edge states, or the corner states, generically, suggesting that the 5D Weyl semimetal is thought of as a physical structural origin of corner states in HOTIs. In addition, we explicitly calculate a nested Wilson loop of the 5D Weyl semimetal and find that the topological structure is identical to that of a Wilson loop of a Dirac monopole.

cond-mat.mes-hall↗

arXiv2020

An Analytic Description of Semi-Classical Black-Hole Geometry

We study analytically the spacetime geometry of the black-hole formation and evaporation. As a simplest model of the collapse, we consider a spherical thin shell, and take the back-reaction from the negative energy of the quantum vacuum state. For definiteness, we will focus on quantum effects of s-waves. We obtain an analytic solution of the semi-classical Einstein equation for this model, that provides an overall description of the black hole geometry form the formation to evaporation. As an application of this result, we find its interesting implication that, after the collapsing shell enters the apparent horizon, the proper distance between the shell and the horizon remains as small as the Planck length even when the difference in their areal radii is of the same order as the Schwarzschild radius. The position of the shell would be regarded as the same place to the apparent horizon in the semi-classical regime of gravity.

hep-th↗

arXiv2020

Nuclear states and spectra in holographic QCD

A new method to study nuclear physics via holographic QCD is proposed. Multiple baryons in the Sakai-Sugimoto background are described by a matrix model which is a low energy effective theory of D-branes of the baryon vertices. We study the quantum mechanics of the matrix model and calculate the eigenstates of the Hamiltonian. The obtained states are found to coincide with known nuclear and baryonic states, and have appropriate statistics and charges. Calculated spectra of the baryon/nucleus for small baryon numbers show good agreement with experimental data. For hyperons, the Gell-Mann--Okubo formula is approximately derived. Baryon resonances up to spin $5/2$ and isospin $5/2$ and dibaryon spectra are obtained and compared with experimental data. The model partially explains even the magic numbers of light nuclei, $N=2,8$ and $20$.

hep-th↗

arXiv2019

Escape from black holes in materials: Type II Weyl semimetals and generic edge states

Type II Weyl semimetals are dictated by bulk excitations with tilted light cones, resembling the inside of black holes. We obtain generic boundary conditions for surface boundaries of the type II Weyl semimetals near Weyl nodes, and show that for a certain boundary condition edge states can escape out of the "black hole" event horizon. This means that for realization of the material "black hole" by the Type II Weyl semimetals a careful choice of the boundary condition is necessary.

cond-mat.mes-hall↗

arXiv2019

Asymptotic States of Black Holes in KMY Model

Following the work of Kawai, Matsuo, and Yokokura, we study the dynamical collapsing process with spherical symmetry in the time-dependent space-time background including the back reaction of Hawking radiation. We show that in this model there are two classes of asymptotic solutions. One of the two classes is known previously. These states have the slope $\partial a/\partial r$ approximately equal to 1. The other class of asymptotic solutions is that of shells with a small thickness. We emphasize that these thin shells should be properly understood as configurations in the low-energy effective theory. They behave characteristically differently from the singular states of ideal thin shells of zero thickness.

hep-th↗