arXiv subjects

Shi-Bei Kong

Publications and source records attributed to Shi-Bei Kong.

18 recordsLinked to original sources

arXiv2026

Temperature of McVittie Black Holes in Cavities

In this paper, we obtain the temperature of the McVittie black hole and the charged McVittie black hole in a cavity with radius $r_c$. The cavity temperature is derived from the black hole Hawking temperature and Kodama vector by using the Tolman relation. We also obtain the cavity temperature of the de Sitter black hole and the charged de Sitter black hole respectively by setting $H^2=Λ/3$ from the above results, which are the same as those from the action method. By the way, we also find that the Kodama vector of the McVittie and charged McVittie black hole is just $\partial/\partial t$, which is very remarkable and interesting. It shows that this method to obtain the cavity temperature is consistent and applicable. It is obvious that this method is much easier than the action method and can be used to similar investigations. It also shows that Kodama vector is very important and useful for dynamical spacetimes.

gr-qc↗

arXiv2026

Investigating Graviton Mass Effects on Black Hole Lensing in dRGT Massive Gravity

In this paper, we delve into the gravitational lensing and photon trajectories in the vicinity of non-asymptotically flat black hole spacetimes within the framework of dRGT massive gravity, incorporating a non-zero graviton mass. We assume that both the observer and the light source are located at a finite distance from the lens object, and calculate the gravitational deflection angle of light ray by such a black hole based on Gauss-Bonnet theorem. Furthermore, we derive the angular radius of Einstein rings associated with black holes in dRGT massive gravity, thereby facilitating a comprehensive discussion on the ramifications of the graviton mass. Notably, our findings reveal pronounced impacts of the graviton mass on both light deflection angles and Einstein ring characteristics, underscoring its significance in dRGT massive gravity and enhancing the detectability of black holes in gravitational lensing observations, thereby opening new avenues for future research.

gr-qc↗

arXiv2025

Effective Pressure of the FRW Universe

In this paper, we study the effective pressure of the $N$-dimensional FRW(Friedmann-Robertson-Walker) universe in Einstein gravity, Gauss-Bonnet gravity, and Lovelock gravity. The effective pressure is defined by $P_{eff}:=-d E/d V$, where $E=ρV$ is the effective energy and $V$ is the volume of the FRW universe inside the apparent horizon. The effective pressure in Einstein gravity is always negative and its absolute value decreases with the horizon radius $R_A$. The effective pressure in Gauss-Bonnet gravity is different with the one in Einstein gravity only when $N\geq6$. In this case, if $α>0$, the effective pressure is always negative, but if $α<0$, it is not always negative and has a minimum. The effective pressure in Lovelock gravity can have multiple zero-points and extreme points. The effective pressure in different dimensions has interesting relations. We also find that under certain condition, the effective pressure is equivalent with the `ordinary' pressure $p$ of the perfect fluid, and this condition do not depend on the specific choice of gravitational theories.

gr-qc↗

arXiv2025

U(1) Gauge Potentials on de Sitter Spacetime

The smooth 1-form Verma module of $\mathfrak{so}(1,4)$ is acquired, which can be regarded as the U(1) gauge potential on de Sitter spacetime. It is shown that electromagnetic fields could not be source free on de Sitter background.

hep-th↗

arXiv2025

Hamiltonian Analysis of 3-dimensional Spacetime in Bondi-like Coordinates

The Hamiltonian analysis for a 3-dimensional connection dynamics of $\frak{so}(1,2)$, spanned by $\{L_{-+},L_{-2},L_{+2}\}$ instead of $\{L_{01}, L_{02}, L_{12}\}$, is first conducted in a Bondi-like coordinate system. The symmetry of the system is clearly presented. A null coframe with 3 independent variables and 9 connection coefficients are treated as basic configuration variables. All constraints and their consistency conditions, the solutions of Lagrange multipliers as well as the equations of motion are presented. There is no physical degree of freedom in the system. The Bañados-Teitelboim-Zanelli (BTZ) spacetime is discussed as an example to check the analysis. Unlike the ADM formalism, where only non-degenerate geometries on slices are dealt with and the Ashtekar formalism, where non-degenerate geometries on slices are mainly concerned though the degenerate geometries may be studied as well, in the present formalism the geometries on the slices are always degenerate though the geometries for the spacetime are not degenerate.

gr-qc↗

arXiv2025

Equation of the Perfect Fluid in the FRW Universe

In this paper, we study the equation of state and its properties of the perfect fluid in the $D$-dimensional FRW universe under Einstein gravity, Gauss-Bonnet gravity and Lovelock gravity. In Einstein gravity, we get the equation of state and find that it has no critical point in the $P$-$V$ diagram, but its isothermal lines have minima in the $4$-dimensional case and are always negative in higher dimensions. In Gauss-Bonnet gravity, we get the equation of state and find that it has a critical point in the $5,6,7,8$-dimensional cases with phase transitions above the critical temperature. In Lovelock gravity, we get the equation of state and conditions of the critical points. Our work shows that both the theories of gravity and the dimensions of the FRW universe affect the existence of the critical point of the perfect fluid. Interestingly, if the critical point exists, phase transition always occures above the critical temperature.

gr-qc↗

arXiv2025

Hamiltonian Analysis of 4-dimensional Spacetime in Bondi-like Coordinates

We discuss the Hamiltonian formulation of gravity in 4-dimensional spacetime under Bondi-like coordinates ${v, r, x^a, a=2, 3}$. In Bondi-like coordinates, the 3-dimensional hypersurface is a null hypersurface and the evolution direction is the advanced time $v$. The internal symmetry group $SO(1,3)$ of the 4-dimensional spacetime is decomposed into $SO(1,1)$, $SO(2)$, and $T^\pm(2)$, whose Lie algebra $so(1,3)$ is decomposed into $so(1,1)$, $so(2)$, $t^\pm(2)$ correspondingly. The $SO(1,1)$ symmetry is very obvious in this kind of decomposition, which is very useful in $so(1,1)$ BF theory. General relativity can be reformulated as the 4-dimensional coframe $(e^I_μ)$ and connection $(ω^{IJ}_μ)$ dynamics of gravity based on this kind of decomposition in the Bondi-like coordinate system. The coframe consists of 2 null 1-forms $e^-$, $e^+$ and 2 spacelike 1-forms $e^2$, $e^3$. The Palatini action is used. The Hamiltonian analysis is conducted by the Dirac's methods. The consistency analysis of constraints has been done completely. There are 2 scalar constraints and one 2-dimensional vector constraint. The torsion-free conditions are acquired from the consistency conditions of the primary constraints about $π^μ_{IJ}$. The consistency conditions of the primary constraints $π^0_{IJ}=0$ can be reformulated as Gauss constraints. The conditions of the Lagrange multipliers have been acquired. The Poisson brackets among the constraints have been calculated. There are 46 constraints including 6 first class constraints $π^0_{IJ}=0$ and 40 second class constraints. The local physical degrees of freedom is 2. The integrability conditions of Lagrange multipliers $n_0$, $l_0$, and $e^A_0$ are Ricci identities. The equations of motion of the canonical variables have also been shown.

gr-qc↗

arXiv2025

Heat Capacity and the Violation of Scaling Laws in Gravitational System

In this paper, we examine the scaling laws in gravitational system from the perspective of free energy landscape and the scaling hypothesis. It has been found that for some special black holes, their critical exponents $(0,1,2,3)$ are beyond the mean field theory, and more surprisingly violate the scaling laws. We find that the main reason for the violation of the scaling laws is that the heat capacity at constant volume $C_V$ is 0, so the critical exponent $α$ is often treated as 0, which can not be derived from the scaling hypothesis. We also find that there is a symmetry violation for the two coexistence states $ω_l$ and $ω_s$.

gr-qc↗

arXiv2025

Thermodynamics of the arbitrary dimensional FRW universe: Joule-Thomson expansion

In this paper, we investigate the thermodynamics especially the Joule-Thomson expansion of the $n$-dimensional FRW (Friedmann-Robertson-Walker) universe with a perfect fluid. We derive the thermodynamic equations of state $P=P(V, T)$ for the $n$-dimensional FRW universe in Einstein gravity and Einstein-Gauss-Bonnet gravity, where the thermodynamic pressure $P$ is defined by the work density $W$ of the perfect fluid, $i.e.$ $P\equiv W$. Furthermore, we present the Joule-Thomson expansion as an application of these equations of state to elucidate the cooling-heating properties of the $n$-dimensional FRW universe. We determine the inversion temperature and inversion pressure in the FRW universe with arbitrary dimensions for the first time, and illustrate the characteristics of inversion curves and isenthalpic curves in the $T$-$P$ plane. We also examine constraints on the perfect fluid in the FRW universe, as derived from the cooling-heating transition point. This study offers insights into deepening our comprehension of cooling and heating regions in the FRW universe, thereby revealing its expansion mechanisms.

gr-qc↗

arXiv2025

Misner-Sharp Energy and P-V Criticality in Quasi-Topological Cosmology

We presented a sound foundation of thermodynamics for a Friedmann-Robertson-Walker (FRW) universe from the first principle in ground-breaking work [Hu et al., JHEP12 (2022) 168]. Based on such an approach, we explore the thermodynamics of cosmology in quasi-topology gravity. Starting from the unified first law, we first obtain the well-defined Misner-Sharp energy in quasi-topology cosmology. We demonstrate that the Misner-Sharp energy is equal to $ρV$ inside the apparent horizon. Further, the unified first law requires extra terms for generalized force and conjugate generalized position, which are identified as thermodynamic pressure and thermodynamic volume, respectively. Hence we naturally derive the equation of state of the FRW universe in quasi-topology gravity, and show that it undergoes $P$-$V$ phase transitions. We calculate the critical exponents for the phase transition, which may be beneficial to probe the micro theory of quasi-topology gravity.

gr-qc↗

arXiv2024

Novel standard candle: Collapsing axion stars

The Hubble constant, $H_0$, is a crucial parameter in cosmology. However, various cosmic observations have produced differing posterior values for $H_0$, resulting in what is referred to as the $H_0$ tension. To resolve this discrepancy, utilizing other cosmological probes to constrain $H_0$ is advantageous. In the quest to identify dark matter candidates, the QCD axion and axionlike particles, collectively referred to as axions, have become leading contenders. These elusive particles can coalesce into dense structures known as axion stars via Bose-Einstein condensation. When these axion stars exceed a critical mass, typically through accretion or merging, they experience a self-induced collapse. This process results in short radio bursts, assuming a decay constant $f_a\lesssim10^{13}{\rm{GeV}}$, with the frequency depending on the axion mass and the luminosity determined by both the axion mass and decay constant. Therefore, we propose that collapsing axion stars could serve as a novel standard candle to constrain $H_0$. Even more interesting is that the radio bursts emitted by collapsing axion stars with specific parameters match the characteristics of observed non-repeating fast radio bursts (FRBs). Thus, FRBs generated by collapsing axion stars have the potential to be used as standard candles to constrain $H_0$.

hep-ph↗

arXiv2024

Cooling-Heating Properties of the FRW Universe in Gravity with a Generalized Conformal Scalar Field

In this paper, within the framework of modified gravity involving a conformal scalar field, we investigate the Joule-Thomson expansion of the FRW universe to identify cooling and heating regions. Notably, we observe that the Joule-Thomson coefficient, denoted as $μ$, diverges at $R_A=\sqrt{-2α}$ when $α<0$, aligning with the thermodynamic singularity of the FRW universe. Additionally, we determine the inversion temperature and inversion pressure for the FRW universe, and illustrate the characteristics of inversion curves and isenthalpic curves in the $T$-$P$ plane. We compare these findings with results obtained under Einstein gravity, discussing the influence of the modification term on the cooling and heating properties of the FRW universe. This work contributes significantly to a deeper understanding of the formation of cooling and heating regions within the FRW universe, thereby advancing our comprehension of the physical mechanisms that govern the expansion of our universe.

gr-qc↗

arXiv2024

Equation of State and Joule-Thomson Expansion for the FRW Universe in the Brane World Scenario

We study the thermodynamic properties of the Friedmann-Robertson-Walker (FRW) universe in the brane world scenario, concentrating on the Randall-Sundrum II model. From the first law of thermodynamics for the FRW universe, we find that the work density W can be identified with the thermodynamic pressure P. We construct the equation of state P=P(V,T) for the FRW universe in the brane world scenario, which does not show P-V phase transition. We further study the Joule-Thomson expansion of the FRW universe, and derive the Joule-Thomson coefficient, which has an inversion point that is affected by the brane tension. These results could provide new ways to test the brane world scenario and extra dimension.

gr-qc↗

arXiv2023

Phase Transitions and Critical Phenomena for the FRW Universe in an Effective Scalar-Tensor Theory

We find phase transitions and critical phenomena of the FRW (Friedmann-Robertson-Walker) universe in the framework of an effective scalar-tensor theory that belongs to the Horndeski class. We identify the thermodynamic pressure (generalized force) $P$ of the FRW universe in this theory with the work density $W$ of the perfect fluid, which is a natural definition directly read out from the first law of thermodynamics. We derive the thermodynamic equation of state $P=P(V, T)$ for the FRW universe in this theory and make a thorough discussion of its $P$-$V$ phase transitions and critical phenomena. We calculate the critical exponents, and show that they are the same with the mean field theory, and thus obey the scaling laws.

gr-qc↗

arXiv2022

First Principle Study of Gravitational Pressure and Thermodynamics of FRW Universe

We make a first principle study of gravitational pressure in cosmic thermodynamics. The pressure is directly derived from the unified first law, in fact the Einstein field equation in spherically symmetric spacetime. By using this pressure, we obtain the thermodynamics for the FRW universe, especially presenting the gravitational equation of state for the FRW spacetime itself, i.e. $P=P(R_A, T)$ for the first time. Furthermore, we study the Joule-Thomson expansion as an application of the thermodynamic equation of state to find the cooling-heating property of the FRW universe. We demonstrate that there is an inversion temperature for a FRW universe if its enthalpy ${\cal H}$ is negative. These investigations shed insights on the evolution of our universe in view of thermodynamics.

gr-qc↗

arXiv2022

The P-V Phase Transition of the FRW Universe

We define thermodynamic pressure $P$ by work density $W$ as the conjugate quantity of thermodynamic volume $V$ from field equation. We derive the equations of state $P$=$P(V, T)$ for the Friedmann-Robertson-Walker (FRW) universe in Einstein gravity and a modified gravity respectively. We find that the equation of state from Einstein gravity shows no $P$-$V$ phase transition, while the equation of state from the modified gravity does, where the critical exponents are the same as those in mean field theory.

gr-qc↗

arXiv2022

The Hawking-Page-like Phase Transition from FRW Spacetime to McVittie Black Hole

In this paper, we investigate the thermodynamics especially the Hawking-Page-like phase transition of the McVittie space-time. We formulate the first law of thermodynamics for the McVittie black hole, and find that the work density $W$ of the perfect fluid plays the role of the thermodynamic pressure, i.e. $P$:=$-W$. We also construct the thermodynamic equation of state for the McVittie black hole. Most importantly, by analysing the Gibbs free energy, we find that the Hawking-Page-like phase transition from FRW spacetime to McVittie black hole is possible in the case $P>0$.

gr-qc↗

arXiv2021

Divergence Behavior of Thermodynamic Curvature Scalar at Critical Point in the Extended Phase Space of Generic Black Holes

The $P$-$V$ phase transition and critical behavior in the extended phase space of asymptotic Anti-de Sitter (AdS) black holes have been widely investigated, in which four critical exponents around critical point are found to be consistent with values in the mean field theory. Recently, another critical exponent $ν$ related to divergent correlation length at critical point is proposed by using thermodynamic curvature scalar $R_N$ in the charged AdS black hole. In this paper, we develop a method to investigate the divergent behavior of $R_N$ at critical point, and find that the divergent behavior of $R_N$ around the critical point expresses a universal property in generic black holes. We further directly apply this method to investigate black holes in de Rham-Gabadadze-Tolley (dRGT) massive gravity to check this universality. Those results shed new lights on the microscopic properties of black holes.

gr-qc↗