arXiv subjects

Alireza Amani

Publications and source records attributed to Alireza Amani.

15 recordsLinked to original sources

arXiv2026

Cosmological Evolution, Analytical Parametrization, and Dynamical Stability of a Bouncing Universe in Non-Minimal Kinetic Coupling Gravity

In this paper, the bouncing cosmology is studied in the framework of the non-minimal kinetic coupling theory between the scalar field and the Einstein tensor. After deriving the modified Friedmann equations and the field equation, by applying the Bounce condition, the system of equations is solved numerically without assuming any analytical form for the scale factor. Thus, the time evolution of the scale factor, the scalar field, and other cosmological quantities are obtained directly from the model dynamics. Then, in order to provide an explicit form for the cosmic evolution, an analytical parameterization for the scale factor is introduced, which is fitted to the numerical solution with high accuracy and its validity is confirmed by comparing the Hubble parameter obtained from the parameterization with the numerical solution. Using this framework, the behavior of cosmological parameters including the Hubble parameter, the comoving Hubble horizon, the energy density, the pressure, and the equation of state (EoS) parameter during the evolution of the universe is investigated, and a smooth transition from the contraction phase to the expansion phase without the occurrence of a singularity is shown. Next, the stability of the model is studied using an autonomous dynamical system and critical point analysis in phase space. The results show that the presented model, in addition to describing a non-singular bouncing scenario, has stable dynamic behavior and the introduced analytical parameterization can be used as a suitable tool for future analytical studies.

gr-qc↗

arXiv2026

Thermodynamics of Deformed AdS-Schwarzschild Black Holes Beyond the Bekenstein Paradigm

This work investigates the thermodynamic behavior of deformed AdS-Schwarzschild black holes by incorporating higher-order corrections within non-interacting spacetime models and extended entropy frameworks. To address the inadequacies of classical statistical mechanics in describing gravitational systems with non-local and long-range interactions, we employ non-extensive entropy formalisms, specifically Tsallis and Barrow entropies, which capture quantum-scale deviations and extended correlations. The resulting thermodynamic analysis reveals significant departures from conventional black hole behavior under strong entropy deformations. Notably, as the degree of non-extensivity decreases, the system asymptotically recovers classical features, indicating an emergent universality across statistical regimes. Furthermore, the Joule-Thomson (JT) expansion is examined to analyze the temperature-pressure response during adiabatic processes. Key thermodynamic quantities, including mass, temperature, heat capacity, Gibbs free energy, enthalpy, internal energy, and the JT coefficient, are computed under the influence of non-extensive entropy corrections. These results provide deeper insight into black hole thermodynamics in quantum-corrected spacetimes and offer new avenues for exploring gravitational systems beyond the traditional Bekenstein-Hawking (BH) framework.

hep-th↗

arXiv2026

Interacting Holographic Dark Energy in $f(Q)$ Gravity: Cosmological Evolution and Gravitational Wave Signatures

In this paper, an interactive Holographic Dark Energy (HDE) model is studied in the framework of modified gravity $f(Q)$. By adopting a power parameterization for the Hubble parameter, the field equations are reconstructed and the evolution of the universe at the background level and tensor perturbations are investigated. Then, using observational data $H(z)$, the model parameters are constrained and the dynamical behavior of dark energy throughout the history of the universe is analyzed. Also, the study of the evolution of energy density, pressure and the Equation of State (EoS) parameter of dark energy shows that dark energy in the late universe naturally tends to a region close to the cosmological constant behavior, while in the past it followed a distinct dynamical evolution. Stability analysis based on the speed of sound also indicates that the model has good classical stability around the present era. In addition, the compatibility of the current values of the relative density parameters of matter and dark energy with the observational constraints confirms the ability of the model to reproduce the main features of the observed universe. Next, the propagation of gravitational waves in the cosmological context of the model is investigated. The results show that the corrections due to $f(Q)$ gravity and the interaction between matter and dark energy can affect the evolution of tensor perturbations and produce signatures distinct from the standard scenario. Overall, the findings of this study indicate that the interactive HDE in the gravitational framework $f(Q)$ can provide a consistent framework for describing the cosmic acceleration and studying the cosmological consequences of gravitational waves.

gr-qc↗

arXiv2026

Correspondence between new agegraphic dark energy and Bose-Einstein condensate dark matter in the context of $f(T)$ gravity

In this paper, we investigate the cosmic evolution within the framework of $f(T)$ gravity using a flat-FRW background and model the universe as consisting of three components: baryonic matter, dark matter, and dark energy. We consider the new agegraphic (NA) as an alternative for dark energy and the Bose-Einstein condensation (BEC) as an alternative for dark matter. After that, first we obtain the Friedman equations and then we obtain the continuity equations in the presence of the interaction term between the dark components of the universe, where the interaction term represents the energy flow from dark matter to dark energy. In what follows, we plot the variation of the cosmological parameters of dark energy in terms of the redshift parameter by using the power-law cosmology. Finally, we investigate the evolution and stability of the universe and report the values of the density parameters of the universe components which confirm the present model with observational data.

gr-qc↗

arXiv2025

Correspondence between particle creation and dark components interaction in the context of $f(\mathcal{G})$ gravity

In this paper, we explore the particle creation scenario in the context of $f(\mathcal{G})$ gravity in flat-FLRW metric. For this purpose, from the perspective of thermodynamics and considering an adiabatic universe, we obtain the modified continuity equation in terms of the dynamic number of particles $N$. On the other hand, we obtain Friedmann's equations in $f(\mathcal{G})$ gravity and then write down the continuity equations of the components of matter and dark energy, taking into account the interaction between them. In what follows, by establishing a correspondence between the particle production scenario and $f(\mathcal{G})$ gravity, we obtain the cosmological parameters in terms of $N$. After that, we find cosmological solutions using power-law cosmology and compare them with Hubble parameter data. Finally, we fit the current model with Hubble data and plot the best fit in terms of the redshift parameter.

gr-qc↗

arXiv2024

Massive Dirac particles based on gapped graphene with Rosen-Morse potential in a uniform magnetic field

We explore the gapped graphene structure in the two-dimensional plane in the presence of the Rosen-Morse potential and an external uniform magnetic field. In order to describe the corresponding structure, we consider the propagation of electrons in graphene as relativistic fermion quasi-particles, and analyze it by the wave functions of two-component spinors with pseudo-spin symmetry using the Dirac equation. Next, to solve and analyze the Dirac equation, we obtain the eigenvalues and eigenvectors using the Legendre differential equation. After that, we obtain the bounded states of energy depending on the coefficients of Rosen-Morse and magnetic potentials in terms of quantum numbers of principal $n$ and spin-orbit $k$. Then, the values of the energy spectrum for the ground state and the first excited state are calculated, and the wave functions and the corresponding probabilities are plotted in terms of coordinates $r$. In what follows, we explore the band structure of gapped graphene by the modified dispersion relation and write it in terms of the two-dimensional wave vectors $K_x$ and $K_y$. Finally, the energy bands are plotted in terms of the wave vectors $K_x$ and $K_y$ with and without the magnetic term.

cond-mat.mes-hall↗

arXiv2023

The interaction of extended Bose-Einstein condensate dark matter with viscous $f(T, B)$ gravity

In this paper, we study the viscous $f(T, B)$ gravity model as a source of dark energy, and the Extended Bose-Einstein Condensate (EBEC) as a source of dark matter, in a flat-FRW metric. In the presence of bulk viscosity, we obtain Friedmann equations and write two continuity equations of dark energy and dark matter by interacting them. Using the generalized Gross-Pitaeveskii equation, we earn Equation of State (EoS) of dark matter by EBEC regime as $p_m = αρ_{m} + βρ_{m}^2$ in which the both of terms are respectively introduced as normal dark matter and dark matter halo. The innovation of the work is that we can simultaneously describe the nature of the dark parts of the universe with the viscous $f(T, B)$ gravity and the EBEC regime, which leads to a deep understanding of the different epochs of the universe from early to late times. In what follows, the energy density and the pressure of dark energy are reconstructed in terms of the redshift parameter, and then we fit the obtained results with 53 supernova data from the Hubble data constraints. Next, we plot the cosmological parameters in terms of the redshift parameter and conclude that the current universe is in an accelerated phase. Finally, we analyze the stability and instability of the current model with the sound speed parameter as well as we draw the density parameter values for dark energy in terms of the redshift parameter.

gr-qc↗

arXiv2022

Observational Hubble parameter data constraints on the interactive model of $f(T)$ gravity with particle creation

In this paper, we consider an open system from the thermodynamic perspective for an adiabatic FRW universe model in which particle creation occurs within the system. In that case, the modified continuity equation is obtained and then we correspond it to the continuity equation of $f(T)$ gravity. So, we take $f(T)$ gravity with the viscous fluid in flat-FRW metric, in which $T$ is the torsion scalar. We consider the contents of the universe to be dark matter and dark energy and consider an interaction term between them. The interesting point of this study is that we make equivalent the modified continuity equation resulting from the particle creation with the matter continuity equation resulting from $f(T)$ gravity. The result of this evaluation creates a relationship between the number of particles and the scale factor. In what follows, we write the corresponding cosmological parameters in terms of the number of particles and also reconstruct the number of particles in terms of the redshift parameter, then We parameterize the Hubble parameter derived from power-law cosmology with 51 data from the Hubble observational parameter. Next, we plot the corresponding cosmological parameters for the dark energy in terms of the redshift to investigate the accelerated expansion of the universe. In addition, by using the sound speed parameter, we discuss the stability analysis and instability analysis of the present model in different eras of the universe. Finally, we plot the density parameter values for dark energy and dark matter in terms of the redshift parameter.

gr-qc↗

arXiv2021

Extended Bose-Einstein condensate dark matter in viscous Gauss-Bonnet gravity

In this paper, we study the $F(R, G)$ gravity model with an interacting model by flat-FRW metric in a viscous fluid. We consider that the universe dominates with components of dark matter and dark energy. This means that the dark matter component derives from Extended Bose-Einstein Condensate (EBEC) and the components of dark energy arise from the $F(R, G)$ gravity. After obtaining the Einstein equation, the energy density and the pressure of dark energy are written in terms of the geometries of the curvature and the Gauss-Bonnet terms, and components of dark matter and viscous fluid. Also, the corresponding continuity equations are written with the presence of interaction terms. In what follows, we employ the EBEC regime instead of the normal dark matter by the dark matter Equation of State (EoS) as $p_{dm} = αρ_{dm} + βρ_{dm}^2$, which arises from the gravitational form. The EoS can be expressed from the perspective of the virial expansion, in which the first and second terms represent normal dark matter and quantum ground state. Next, the corresponding Friedmann equations reconstruct in terms of the redshift parameter, then by using the scenario of the power-law cosmology for the scale factor, we fit the present model with the Hubble amounts of 51 supernova data by the likelihood analysis. In that case, we acquire the cosmological parameters of dark energy in terms of the redshift parameter, and by plotting these graphs, we see that the universe is currently undergoing an accelerated expansion phase. Finally, we investigate the stability of the present model with the sound speed parameter.

gr-qc↗

arXiv2021

Viscous interacting and stability on dark matter Bose-Einstein condensation with modified Chaplygin gas

In this paper, the viscous cosmological dynamics are studied in the presence of dark matter Bose-Einstein Condensation (BEC) by curved-FRW background. For this purpose, we use the BEC regime rather than the normal dark matter (the cold dark matter or the barotropic dark matter) with the dark matter Equation of State (EoS) as $p_{dm} \propto ρ_{dm}^2$, which arises from the gravitational form. Therefore, we obtain the corresponding continuity equations with the existence of the universe components by considering an interacting model with modified Chaplygin gas. Afterward, we derive the energy density and the pressure of dark energy in terms of the redshift parameter. And then, by introducing a parametrization function and fitting it with 51 supernova data with the likelihood analysis, we find the cosmological parameters versus redshift parameter. In what follows, we plot the corresponding dynamic graphs proportional to redshift, and then we represent the universe is currently undergoing an accelerated expansion phase. Finally, we explore the stability and the instability of the present model with the sound speed parameter.

gr-qc↗

arXiv2021

Energy spectrum of massive Dirac particles in gapped graphene with Morse potential

In this paper, we study the massive Dirac equation with the presence of the Morse potential in polar coordinate. The Dirac Hamiltonian is written as two second-order differential equations in terms of two spinor wavefunctions. Since the motion of electrons in graphene is propagated like relativistic fermionic quasi-particles, then one is considered only with pseudospin symmetry for aligned spin and unaligned spin by arbitrary $k$. Next, we use the confluent Heun's function for calculating the wavefunctions and the eigenvalues. Then, the corresponding energy spectrum obtains in terms of $N$ and $k$. Afterward, we plot the graphs of the energy spectrum and the wavefunctions in terms of $k$ and $r$, respectively. Moreover, we investigate the graphene band structure by a linear dispersion relation which creates an energy gap in the Dirac points called gapped graphene. Finally, we plot the graph of the valence and conduction bands in terms of wavevectors.

quant-ph↗

arXiv2020

Observational constraints and stability in viscous $f(T,\mathcal{T})$ gravity

In this paper, we study the $f(T,\mathcal{T})$ gravity model in the presence of the bulk viscosity by the flat-FRW metric. The field equation is obtained by teleparallel gravity with tetrad field. The universe components are considered as matter and dark energy which the dark energy component associates from the viscous $f(T,\mathcal{T})$ gravity. After calculating the Friedmann equations, we obtain the energy density, the pressure and the EoS of dark energy in terms of the redshift parameter. Afterward, we plot the corresponding cosmological parameters versus the redshift parameter and examine the accelerated expansion of the universe. In the end, we explore the system stability by a function called the speed sound parameter.

gr-qc↗

arXiv2020

Thermodynamics of the viscous $f(T, B)$ gravity in the new agegraphic dark energy model

In this paper, we first obtain the energy density by the approach of the new agegraphic dark energy model, and then the $f(T,B)$ gravity model is studied as an alternative to the dark energy in a viscous fluid by flat-FRW background, in which $T$ and $B$ are torsion scalar and boundary term. The Friedmann equations will obtain in the framework of modified teleparallel gravity by tetrad components. We consider that the universe dominates with components such as matter and dark energy by an interacting model. The Hubble parameter is parameterized by the power-law for the scale factor, and then we fit the corresponding Hubble parameter with observational data constraints. The variation of the equation of state (EoS) for dark energy is plotted as a function of the redshift parameter, and the accelerated expansion of the universe is explored. In what follows, the stability of the model is also studied on the base of the sound speed parameter. Finally, the generalized second law of thermodynamics is investigated by entropies of inside and on the boundary of the apparent horizon in thermodynamics equilibrium.

gr-qc↗

arXiv2019

Thermodynamics and stability of $f(T,B)$ gravity with viscous fluid by observational constraints

In this paper, we study the model of $f(T, B)$ gravity with viscous fluid in flat-FRW metric, in which $T$ and $B$ are torsion scalar and boundary term, respectively. We obtain the Friedmann equations in the framework of modified teleparallel gravity by tetrad components. We consider an interacting model between matter and dark energy so that universe dominates by viscous fluid. Then, we write the corresponding cosmological parameters in terms of the redshift parameter, and, we parameterize the Hubble parameter with experimental data. In what follows, we plot the corresponding cosmological parameters for dark energy components in terms of redshift, thereafter we investigate the accelerated expansion of the universe. Moreover, we discuss the stability of the model by using the sound speed parameter. Finally, we investigate the validity of the generalized second law of thermodynamics.

gr-qc↗

arXiv2017

Stability and interacting $f(T,\mathcal{T})$ gravity with modified Chaplygin gas

In this paper, the model of interaction is studied between $f(T,\mathcal{T})$ gravity and modified Chaplygin gas in FRW-flat metric. We obtain the Friedmann equations in the framework of teleparallel gravity by vierbein field. We consider that Universe dominates by components of cold matter, dark energy and modified Chaplygin gas. In what follows we separately write the corresponding continuity equations for components of Universe. Also, dark energy EoS and effective EoS are obtained with respect to redshift, thereafter the corresponding cosmological parameters are plotted in terms of redshift, thereinafter the accelerated expansion of the Universe is investigated. Finally, the stability of the model is discussed in phase plane analysis.

gr-qc↗