arXiv subjects

Babak Vakili

Publications and source records attributed to Babak Vakili.

At least 19 recordsLinked to original sources

arXiv2026

Classical and quantum perspectives on temperature in accelerated frames

We study the notion of temperature in uniformly accelerated frames within a relativistic thermodynamic framework. Considering a perfect fluid at rest in a non-inertial (Rindler) frame, we derive the condition for thermal equilibrium from energy--momentum conservation. This leads to a position-dependent temperature profile consistent with the Tolman--Ehrenfest relation. We emphasize that this temperature characterizes the local thermodynamic equilibrium of the fluid in the accelerated frame and does not arise from a transformation law between different observers. The physical interpretation of the result and its relation to acceleration-induced effects are briefly discussed.

gr-qc↗

arXiv2026

Relativistic transformation of temperature for exotic cosmological fluids

We study the relativistic transformation of temperature for effective cosmological fluids with negative pressure within a covariant thermodynamic framework. The Lorentz transformation of temperature is derived for barotropic fluids with $p=wρ$ and for the (generalized) Chaplygin gas with $p=-A/ρ^α$. For barotropic fluids with constant negative equation-of-state parameter, we show that negative pressure suppresses the growth of temperature under relativistic boosts. In contrast, the Chaplygin gas exhibits a qualitatively different behavior due to its density-dependent pressure, leading to a monotonic increase of the transformed temperature with velocity. The dependence of the relativistic temperature on the relative velocity and background energy density is illustrated through representative examples.

gr-qc↗

arXiv2026

Affine quantization of the dynamical Reissner--Nordström region

We study the quantum dynamics of the dynamical region of the Reissner--Nordström geometry using a minisuperspace reduction and affine quantization, which is naturally suited for positive-definite geometrical variables. The resulting Wheeler--DeWitt equation becomes separable, yielding Hermite-polynomial modes in one sector and Gaussian-like radial solutions in the other. Affine quantization introduces additional short-distance contributions that modify the small-radius behaviour of the wave function. By constructing normalizable semiclassical wave packets, we analyze the resulting probability distributions in minisuperspace and the role played by the electric charge in the quantum dynamics. Our results extend previous affine-quantization studies of the Schwarzschild case to the charged Reissner--Nordström geometry.

gr-qc↗

arXiv2026

Kinematical correlations via $κ$-Poincaré coproducts

We study a kinematical consequence of the Hopf-algebraic momentum composition law in $κ$-Minkowski spacetime. The same curved momentum space can be described in different coordinates. In the bicrossproduct basis the ordered-plane-wave labels are the translation-generator eigenvalues, so the relevant map is one-to-one. In the classical basis, instead, the translation eigenvalues $P_μ$ are nonlinearly related to the ordered-plane-wave labels $p_μ$. This relation can fail to be globally one-to-one in a high-momentum region. When a given classical-basis four-momentum admits more than one real auxiliary preimage, the branch-sensitive quantity $P_+\equiv P_0+P_4=κe^{p_0/κ}$ enters the coproduct and resolves the branches in two-particle states. Imposing the vanishing total-momentum constraint therefore gives branch-dependent $κ$-deformed back-to-back momentum correlations. In a single-branch regime this is just a deformed correlated product, while in a multibranch regime a state specified only by $P_μ$ can be expanded into distinct auxiliary branches. If $P_μ$ are taken as the directly meaningful momenta, the physical content is the resulting deformed correlation pattern. If the auxiliary variables $p_μ$ are assigned operational meaning, the same constrained state can be interpreted as a superposition over different auxiliary branches. We also compare this structure with standard regular self-adjoint nonrelativistic minimal-length models and find no analogous smooth local two-real-branch inversion on their physical domains.

hep-th↗

arXiv2026

Relativistic transformation of temperature revisited

The relativistic transformation of temperature has long remained controversial, with the classical laws of Planck-Einstein, Ott-Eddington-Moller and Landsberg yielding conflicting results. We reexamine this issue from a relativistic thermodynamic and statistical perspective, starting from the energy-momentum tensor of an isotropic system and defining the effective temperature Teff as that inferred by a moving observer from the transformed energy density. Analyses of a photon gas, a relativistic ideal gas and an electron gas show that Teff consistently increases with velocity, supporting the Ott-Eddington interpretation while depending on the system's equation of state. These results indicate that temperature is not a Lorentz-invariant scalar but an observer-dependent quantity. A consistent relativistic description emerges when temperature is related to the inverse-temperature four-vector beta, linking operational and invariant viewpoints within a unified thermodynamic framework.

gr-qc↗

arXiv2026

Chaos and epoch structure in the deformed Mixmaster universe

We study the dynamics of the Bianchi~IX (Mixmaster) universe under classical polymerization and generalized uncertainty principle (GUP) deformation of the Poisson brackets. Starting from the Misner Hamiltonian, we derive the effective equations of motion with both modifications and analyze the duration of Kasner epochs as a probe of dynamical behavior. Our results show that GUP corrections typically shorten the epochs, leading to more frequent wall collisions, whereas polymer corrections prolong them and suppress successive bounces. At leading order, the combined deformation produces an additive shift that interpolates between these two trends. While the billiard picture remains robust, the strength of Mixmaster chaos becomes sensitive to the deformation parameters. These results illustrate how Planck-scale corrections may either enhance or suppress cosmological chaos, offering a controlled framework for exploring early-universe dynamics.

gr-qc↗

arXiv2026

Quantum teleportation in expanding FRW universe

We investigate the process of quantum teleportation in an expanding universe modeled by Friedmann-Robertson-Walker spacetime, focusing on two cosmologically relevant scenarios: a power-law expansion and the de Sitter universe. Adopting a field-theoretical approach, we analyze the quantum correlations between two comoving observers who share an entangled mode of a scalar field. Using the Bogoliubov transformation, we compute the teleportation fidelity and examine its dependence on the expansion rate, initial entanglement, and the mode frequency. Our findings indicate that spacetime curvature and the underlying cosmological background significantly affect the efficiency of quantum teleportation, particularly through mode mixing and vacuum structure. We also compare our results with the flat Minkowski case to highlight the role of cosmic expansion in degrading or preserving quantum information.

quant-ph↗

arXiv2026

A two-mode model for black hole evaporation and information flow

We develop and analyze a two-oscillator model for black hole evaporation in which an effective geometric degree of freedom and a representative Hawking radiation mode are described by coupled harmonic oscillators with opposite signs in their free Hamiltonians. The normal-mode structure is obtained analytically and the corresponding modal amplitudes determine the pattern of energy exchange between the two sectors. To bridge the discrete and semiclassical pictures, we introduce smooth envelope functions that provide a continuous effective description along the geometric variable. Numerical simulations in a truncated Fock space show that the two oscillators exchange quanta in an approximately out-of-phase manner, consistent with an effective conservation of $\langle n_x\rangle - \langle n_y\rangle$. The reduced entropy $S_x(t)$ exhibits periodic growth, indicating entanglement generation. These results demonstrate that even a minimal two-mode framework can capture key qualitative features of energy transfer and information flow during evaporation.

quant-ph↗

arXiv2025

Classical Polymerization of the Bianchi I Model with Deformed Poisson Structure

We study the dynamics of the Bianchi~I cosmological model in the presence of both polymer quantization effects and an exponential deformation of the Poisson algebra. Starting from the Hamiltonian formulation, we derive the polymer-deformed equations of motion and analyze their solutions for the contracting branch of the model. In contrast with the undeformed classical dynamics, the exponential deformation with suitable values of deformation parameters, produces a noticeably slower evolution of the volume variable and leads to a stabilization of the anisotropy parameters, which remain bounded throughout the evolution. No removal of the initial singularity is observed; however, the deformation significantly modifies the asymptotic behavior, offering a mechanism to suppress anisotropic shear near the singularity. Our results are illustrated through analytic solutions, highlighting the qualitative differences between the standard and the polymer--deformed Bianchi~I cosmology.

gr-qc↗

arXiv2025

Affine Quantization of the Interior Schwarzschild Black Hole

In this paper, we investigate the Hamiltonian formulation of a spherically symmetric spacetime that corresponds to the interior of a Schwarzschild black hole. The resulting phase space involves two independent dynamical variables along with their conjugate momenta. We quantize the associated minisuperspace using the affine quantization method, which is particularly suited for systems with positive-definite configuration variables. We then explore whether the quantum effects encoded in this wave function can lead to the avoidance of classical singularities.

gr-qc↗

arXiv2023

Bi-directional quantum teleportation of GHZ-like states

In this paper we propose a method through which $n$-qubit states can simultaneously be bi-directionally transmitted between two users. We assume that Alice and Bob, the legitimate users, each have a $n$-qubit GHZ-like state and want to teleport it to the other party. Also, a four-qubit cluster state plays the role of the quantum channel of this bi-directional quantum teleportation. The protocol is based on the method that at first, each user, through a series of $\mbox{CNOT}$ gates, converts the $n$-qubit state into a single qubit and some $0$ qubits. Then, by means of the Bell state measurement and proper operation, the single qubit state is transferred over the channel between the two sides. By re-applying the $\mbox{CNOT}$ gates on the transmitted qubits and auxiliary $0$ states, each user reconstructs the initial GHZ-like state. Finally, we investige the effects of some kind of noises on the density marix of the channel due to its interaction with the environment and present a method to protect the channel against the bit-flip error.

quant-ph↗

arXiv2021

Hořava-Lifshitz scalar field cosmology: classical and quantum viewpoints

In this paper, we study a projectable Hořava-Lifshitz cosmology without the detailed balance condition minimally coupled to a non-linear self-coupling scalar field. In the minisuperspace framework, the super Hamiltonian of the presented model is constructed by means of which, some classical solutions for scale factor and scalar field are obtained. Since these solutions exhibit various types of singularities, we came up with the quantization of the model in the context of the Wheeler-DeWitt approach of quantum cosmology. The resulting quantum wave functions are then used to investigate the possibility of the avoidance of classical singularities due to quantum effects which show themselves important near these singularities.

gr-qc↗

arXiv2019

Bianchi type I, Schutz perfect fluid and evolutionary quantum cosmology

We study the classical and quantum cosmology of a universe in which the matter content is a perfect fluid and the background geometry is described by a Bianchi type I metric. To write the Hamiltonian of the perfect fluid we use the Schutz representation, in terms of which, after a particular gauge fixing, we are led to an identification of a clock parameter which may play the role of time for the corresponding dynamical system. In view of the classical cosmology, it is shown that the evolution of the universe represents a late time expansion coming from a big-bang singularity. We also consider the issue of quantum cosmology in the framework of the canonical Wheeler-DeWitt (WDW) equation. It is shown that the Schutz formalism leads to the introduction of a momentum that enters linearly into Hamiltonian. This means that the WDW equation takes the form of a Schrödinger equation for the quantum-mechanical description of the model under consideration. We find the eigenfunctions and with the use of them construct the closed form expressions for the wave functions of the universe. By means of the resulting wave function we evaluate the expectation values and investigate the possibility of the avoidance of classical singularities due to quantum effects. We also look at the problem through Bohmian approach of quantum mechanics and while recovering the quantum solutions, we deal with the reason of the singularity avoidance by introducing quantum potential.

gr-qc↗

arXiv2018

Polymer deformation and particle tunneling from Schwarzschild black hole

In this paper, we investigate a tunneling mechanism of massless particles from the Schwarzschild black hole in the framework of polymer quantum mechanics. According to the corresponding invariant Liouville volume, we determine the tunneling rate from Schwarzschild black hole by the polymeric quantization procedure. In this regard, we show that the temperature and tunneling radiation of the black hole receive new corrections in such a way that the exact radiant spectrum is no longer precisely thermal.

gr-qc↗

arXiv2018

SO(4; 2) and derivatively coupled dRGT massive gravity

In this paper we study the possibility of assigning a geometric structure to the Lie groups. It is shown the Poincaré and Weyl groups have geometrical structure of the Riemann-Cartan and Weyl space-time respectively. The geometric approach to these groups can be carried out by considering the most general (non)metricity conditions, or equivalently, tetrad postulates which we show that can be written in terms of the group's gauge fields. By focusing on the conformal group we apply this procedure to show that a nontrivial 3-metrics geometry may be extracted from the group's Maurer-Cartan structure equations. We systematically obtain the general characteristics of this geometry, i.e. its most general nonmetricity conditions, tetrad postulates and its connections. We then deal with the gravitational theory associated to the conformal group's geometry. By proposing an Einstein-Hilbert type action, we conclude that the resulting gravity theory has the form of quintessence where the scalar field derivatively coupled to massive gravity building blocks.

gr-qc↗

arXiv2018

Classical polymerization of the Schwarzschild metric

We study a spherically symmetric setup consisting of a Schwarzschild metric as the background geometry in the framework of classical polymerization. This process is an extension of the polymeric representation of quantum mechanics in such a way that a transformation maps classical variables to their polymeric counterpart. We show that the usual Schwarzschild metric can be extracted from a Hamiltonian function which in turn, gets modifications due to the classical polymerization. Then, the polymer corrected Schwarzschild metric may be obtained by solving the polymer-Hamiltonian equations of motion. It is shown that while the conventional Schwarzschild space-time is a vacuum solution of the Einstein equations, its polymer-corrected version corresponds to an energy-momentum tensor that exhibits the features of dark energy. We also use the resulting metric to investigate some thermodynamical quantities associated to the Schwarzschild black hole, and in comparison with the standard Schwarzschild metric the similarities and differences are discussed.

hep-th↗

arXiv2017

A new holographic dark energy model in Brans-Dicke theory with logarithmic scalar field

We study a holographic dark energy model in the framework of Brans-Dicke (BD) theory with taking into account the interaction between dark matter and holographic dark energy. We use the recent observational data sets, namely SN Ia compressed Joint Light-Analysis(cJLA) compilation, Baryon Acoustic Oscillations (BAO) from BOSS DR12 and the Cosmic Microwave Background (CMB) of Planck 2015. After calculating the evolution of the equation of state as well as the deceleration parameters, we find that with a logarithmic form for the BD scalar field the phantom crossing can be achieved in the late time of cosmic evolution. Unlike the conventional theory of holographic dark energy in standard cosmology ($ω_D=0$), our model results a late time accelerated expansion. It is also shown that the cosmic coincidence problem may be resolved in the proposed model. We execute the statefinder and Om diagnostic tools and demonstrate that interaction term does not play a significant role. Based on the observational data sets used in this paper it seems that the best value with $1σ$ and $2σ$ confidence interval are $Ω_m=0.268^{+0.008~+0.010}_{-0.007~-0.009}$, $ α=3.361^{+0.332~+0.483}_{-0.401~-0.522}$, $β=5.560^{+0.541~+0.780}_{-0.510~-0.729}$, $c=0.777^{+0.023~+0.029}_{-0.017~-0.023}$ and $b^2 =0.045$, according to which we find that the proposed model in the presence of interaction is compatible with the recent observational data.

astro-ph.CO↗

arXiv2015

Closed-form solutions of the Wheeler-DeWitt equation in a scalar-vector field cosmological model by Lie symmetries

We apply as selection rule to determine the unknown functions of a cosmological model the existence of Lie point symmetries for the Wheeler-DeWitt equation of quantum gravity. Our cosmological setting consists of a flat Friedmann-Robertson-Walker metric having the scale factor $a(t)$, a scalar field with potential function $V(ϕ)$ minimally coupled to gravity and a vector field of its kinetic energy is coupled with the scalar field by a coupling function $f(ϕ)$. Then, the Lie symmetries of this dynamical system are investigated by utilizing the behavior of the corresponding minisuperspace under the infinitesimal generator of the desired symmetries. It is shown that by applying the Lie symmetry condition the form of the coupling function and also the scalar field potential function may be explicitly determined so that we are able to solve the Wheeler-DeWitt equation. Finally, we show how we can use the Lie symmetries in order to construct conservation laws and exact solutions for the field equations.

gr-qc↗