arXiv subjects

Haximjan Abdusattar

Publications and source records attributed to Haximjan Abdusattar.

15 recordsLinked to original sources

arXiv2026

The FRW Universe as a van der Waals-like Thermodynamic Heat Engine

It is well known that the Friedmann-Robertson-Walker (FRW) universe is a dynamical spacetime, and it has thermodynamics embodied on the apparent horizon. Notably, it also possesses a van der Waals-like equation of state, enabling us to consider thermodynamic cycles and explore the potential of the FRW universe as a heat engine. In this paper, we investigate two types of cycle--the Carnot cycle and the rectangular cycle--based on the phase diagram derived from the equation of state, to study the heat engine characteristics of the FRW universe. Furthermore, we calculate the work done and assess the corresponding efficiencies, illustrating the efficiency diagram for the FRW universe's heat engine. We observe that the efficiency of the rectangular cycle consistently remains below unity and never exceeds the Carnot efficiency--the thermodynamic upper limit. This finding is in alignment with the traditional thermodynamic principles that govern heat engines.

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↗

arXiv2026

Thermodynamic curvature in phase transitions for Hayward AdS black hole

We investigate $P$-$V$ criticality, with a focus on Ruppeiner geometry, in the extended phase space of Hayward anti-de Sitter (AdS) black holes. Through thermodynamic analysis, we confirm that Hayward-AdS black holes undergo distinct $P$-$V$ phase transitions and exhibit well-defined critical phenomena in the vicinity of their critical points. These behaviors are characterized by four critical exponents that typically obey the scaling laws predicted by mean-field theory--indicating a consistent thermodynamic framework with classical phase transition systems ($e.g.,$ van der Waals fluids). Furthermore, we employ Ruppeiner geometry to probe the thermodynamic fluctuations of Hayward-AdS black holes, and by calculating the corresponding curvature scalar, we gain direct insights into the interaction nature of the black hole's microscopic constituents.

gr-qc↗

arXiv2025

Insight into the Microstructures of Black Holes with Quantum-Triggered Violations

In this study, we investigate the microstructures of a charged AdS (Anti-de Sitter) black hole exhibiting quantum anomalies through the lens of Ruppeiner geometry. Previous research has established that black holes undergo $P$-$V$ phase transitions and exhibit critical phenomena near their critical points, characterized by four critical exponents that typically obey scaling laws predicted by mean-field theory. However, recent findings have revealed that black holes with quantum anomalies can violate these scaling laws. Motivated by these discoveries, we employ Ruppeiner geometry to probe the thermodynamic fluctuations and gain insights into the microstructure of such black holes. Our analysis aims to elucidate how quantum effects modify the microscopic properties of spacetime, offering a novel perspective on the understanding of black hole thermodynamics.

gr-qc↗

arXiv2025

Nucleon axial form factors in generalized nonlocal chiral effective theory

In this work, we first investigate the chiral transformation properties of the nonlocal pion field operator and construct a generalized nonlocal chiral Lagrangian that is invariant under $\mathrm{SU}(2)$ chiral symmetry transformations. As a simple application, we then calculate the leading and next-leading order pion one loop corrections to the nucleon axial form factors within nonlocal chiral perturbation theory. Then, we fit the next leading order and next-next leading order low energy coupling constants (LECs) to lattice QCD data. The fitted results show that the nonlocal LECs are comparatively smaller than their local counterparts. Finally, using these LECs, we compute the $Q^{2}$ dependence of the nucleon axial form factors. The numerical results indicate that the nonlocal nucleon axial form factors are consistent with lattice QCD data in a wide $\rm Q^{2}$ range, up to $\rm Q^{2} = 1~\mathrm{GeV}^{2}$

hep-ph↗

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↗

arXiv2024

Phase transitions, critical behavior and microstructure of the FRW universe in the framework of higher order GUP

In this paper, we explore the the phase transition, critical behavior and microstructure of the FRW in the framework of a new higher order generalized uncertainty principle. Our initial step involves deriving the equation of state by defining the work density $W$ from GUP-corrected Friedmann equations as the thermodynamic pressure $P$. Based on the modified equation of state, we conduct an analysis of the $P-V$ phase transition in the FRW universe. Subsequently, we obtain the critical exponents and coexistence curves for the small and large phases of the FRW universe around the critical point. Finally, employing Ruppeiner geometry, we derive the thermodynamic curvature scalar $R_N$, investigating its sign-changing curve and spinodal curve. The results reveal distinctive thermodynamic properties for FRW universes with positive and negative GUP parameters $β$. In the case of $β>0$, the phase transition, critical behavior and microstructure of FRW universe are consistent with those of Van der Waals fluids. Conversely, for $β<0$, the results resemble those obtained through effective scalar field theory. These findings underscore the capacity of quantum gravity to induce phase transitions in the universe, warranting further in-depth exploration.

gr-qc↗

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

Insight into the Microstructure of FRW Universe from a $P$-$V$ Phase Transition

The $P$-$V$ phase transition of the FRW (Friedmann-Robertson-Walker) universe with a perfect fluid has recently been investigated, revealing that the four critical exponents near the critical point are consistent with the values predicted by mean field theory. Notably, the coexistence phase of the $P$-$V$ phase transition in the FRW universe above the critical temperature, which distinguishes it from van der Waals system and most of AdS black holes system. This unique property allows us to investigate the microstructure of the FRW universe as a thermodynamic system. Our analysis of the Ruppeiner geometry for the FRW universe reveals that the behavior of the thermodynamic scalar curvature near criticality is characterized by a dimensionless constant identical to that of the van der Waals fluid. Additionally, we observe that while repulsive interactions dominate for the coexistence samll phase with higher temperature, the scalar curvature for the coexistence large phase is always negative, indicating attractive interactions, providing new insights into the nature of interactions among the perfect fluid matter constituents in the expanding FRW universe.

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↗

arXiv2016

Abundance of Asymmetric Dark Matter in Brane World Cosmology

Relic abundance of asymmetric Dark Matter particles in brane world cosmological scenario is investigated in this article. Hubble expansion rate is enhanced in brane world cosmology and it affects the relic abundance of asymmetric Dark Matter particles. We analyze how the relic abundance of asymmetric Dark Matter is changed in this model. We show that in such kind of nonstandard cosmological scenario, indirect detection of asymmetric Dark Matter is possible if the cross section is small enough which let the anti--particle abundance kept in the same amount with the particle. We show the indirect detection signal constraints can be used to such model only when the cross section and the 5 dimensional Planck mass scale are in appropriate values.

hep-ph↗