arXiv subjects

J. Sadeghi

Publications and source records attributed to J. Sadeghi.

At least 19 recordsLinked to original sources

arXiv2026

Striving to find a bridge between noncommutative and generalized entropy parameters in the harmonic oscillator dynamics

In this study, we use the harmonic oscillator s energy spectrum to connect its dynamical behavior to the formalism of statistical mechanics through entropy. We perform a thermal analysis of the entropy generated by this spectrum in both commutative and noncommutative two-dimensional configuration spaces, employing the Tsallis and Renyi entropy measures. The primary objective is to examine the possibility of an intrinsic link and mutual influence between the noncommutative parameter({\theta}) and the parameters arising from generalized entropies. By analyzing both Tsallis and Renyi frameworks, we investigate whether a fundamental relationship exists between {\theta} and the entropy index q. Establishing such a connection could provide new insights into the interplay between spacetime geometry and generalized statistical mechanics.

physics.gen-ph↗

arXiv2026

Geometry-Induced Termination of the Repetitive Penrose Process in Rotating Simpson-Visser Black Holes

We examine the Repetitive Penrose Process in the rotating Simpson-Visser spacetime, whose parameter space includes regular black holes, black-bounce geometries, and traversable wormholes. Assuming that the regularization parameter remains unchanged throughout the evolution, the analysis shows that the endpoint of the repetitive process is not always determined solely by the conventional minimum spin condition. Instead, for sufficiently large values of the regularization parameter, the evolving solution may leave the parameter domain corresponding to the original two horizon black hole branch before the dynamical spin limit is reached. Within the present framework, this provides an additional geometry-induced condition that limits the continuation of the iterative sequence. The numerical results further show that the relative importance of the dynamical and geometry-induced termination mechanisms depends sensitively on the regularization parameter. For small deformations, the evolution remains qualitatively similar to that of the Kerr spacetime. As the regularization parameter increases, however, the cumulative extracted energy, the number of admissible Penrose iterations, and the efficiency of the process are progressively reduced. We also examine how the extracted energy, the final irreducible mass, and two complementary efficiency measures vary with both the regularization parameter and the particle decay radius. Overall, the present analysis indicates that, within the RSV geometry, the underlying spacetime structure influences not only the cumulative efficiency of the repetitive Penrose process but also the parameter range over which the iterative evolution remains self-consistent. These results highlight the role that spacetime geometry can play in shaping the long-term evolution of idealized Penrose-type energy extraction processes in regular rotating black-hole spacetimes.

gr-qc↗

arXiv2026

Beyond the Bounce: Multiple Tidal Sign Reversals and Turning-Point Bifurcations in Multi-Horizon Black Holes

We investigate the radial motion and tidal forces experienced by neutral test particles in multi-horizon black hole solutions arising from Einstein gravity coupled to nonlinear electrodynamics (NED). Focusing on the three- and four-horizon configurations, we examine how nonlinear electromagnetic corrections modify the causal structure, radial geodesic motion, and tidal-force profiles in comparison with the Schwarzschild and Reissner-Nordstrom (R-N) spacetimes. Our analysis shows that the NED field gives rise to multiple zero crossings in both the radial and angular tidal-force components, leading to successive transitions between stretching and compressive tidal regimes. More importantly, the radial equation of motion contains classically forbidden regions bounded by bounce-back points. For the class of trajectories considered in this work, these forbidden regions prevent particles from entering the spacetime domain where the tidal forces become divergent. In the super-extremal regime admitted by these solutions, the forbidden region may extend beyond the event horizon, preventing particles released from rest at sufficiently large distances from crossing the horizon. We further identify a systematic ordering of the critical charge values associated with the appearance of tidal-force zero crossings, additional horizons, and bounce-back points. For both the three- and four-horizon configurations, these critical values satisfy a hierarchical ordering, indicating that changes in the tidal-force structure precede the corresponding modifications of the horizon configuration. These results demonstrate that nonlinear electrodynamics can substantially modify the classical dynamics of neutral particles in multi-horizon black hole spacetimes through the combined effects of forbidden regions, multiple tidal transitions, and changes in the horizon structure.

gr-qc↗

arXiv2025

The Influence of Stable Photon Sphere Advent on Orbital Precession in moving towards the Extremality

In this work, we investigate the behaviour of the periapsis shift in static charged black-hole spacetimes, focusing on the interplay between extremality and the Aschenbach-like effect. We first examine the evolution of orbital dynamics as the extremal limit is approached in representative charged black-hole models. We then extend the analysis to black-hole geometries that admit a stable photon sphere outside the event horizon, where the Aschenbach-like effect has previously been identified. Our results show that the periapsis shift remains a well-defined dynamical quantity in the extremal regime and continuously reflects changes in the underlying spacetime geometry. For black-hole solutions possessing an external stable photon sphere, the associated minimum of the effective potential produces characteristic modifications in both the angular-velocity profile and the periapsis shift. When extremality and the Aschenbach-like effect coexist, the orbital dynamics undergo a qualitative transition, giving rise to a three-region structure consisting of an inner prograde region, an intermediate retrograde region, and an outer prograde region. Within the black-hole models investigated in this work, such behaviour is absent from the other configurations considered. These results demonstrate that the periapsis shift provides a sensitive dynamical probe of strong-field black-hole spacetimes, encoding both geometric and orbital information beyond that obtained from photon-sphere analyses alone. Our findings highlight the rich orbital structure that can emerge from the combined presence of extremality and an external stable photon sphere and provide a useful framework for future studies of orbital dynamics in modified theories of gravity.

gr-qc↗

arXiv2024

Investigation of thermal properties of Hulthén potential from statistical and superstatistical perspectives with various distributions

The Hulthén potential is a short-range potential that has been widely used in various fields of physics. In this paper, we investigate the distribution functions for the Hulthén potential by using statistical and superstatistical methods. We first review the ordinary statistics and superstatistics methods. We then consider some distribution functions, such as uniform, 2-level, gamma, and log-normal and F distributions. Finally, we investigate the behavior of the Hulthén potential for statistical and superstatistical methods and compare the results with each other. We use the Tsallis statistics of the superstatistical system. We conclude that the Tsallis behavior of different distribution functions for the Hulthén potential exhibits better results than the statistical method. We examined the thermal properties of the Hulthén potential for five different distributions: Uniform, 2-level, Gamma, Log-normal, and F. We plotted the Helmholtz free energy and the entropy as functions of temperature for various values of q. It shows that the two uniform and 2-level distributions have the same results due to the universal relationship and that the F distribution does not become ordinary statistics at q=1. It also reveals that the curves of the Helmholtz free energy and the entropy change their order and behavior as q increases and that some distributions disappear or coincide at certain values of q. One can discuss the physical implications of our results and their applications in nuclear and atomic physics in the future.

cond-mat.stat-mech↗

arXiv2023

de Sitter Swampland Conjecture in String Field Inflation

In this paper, we study a particular type of inflation by using non-local Friedman equations that are somehow derived from the zero levels of string field theory and express a tachyonic action. Then, we challenge it by further refining de Sitter (dS) swampland conjecture (FRdSSC) monitoring. Therefore, we investigate some quantities, such as potential and Hubble parameters. We also consider slow-roll parameters to examine quantities such as the scalar spectrum index and the tensor-to-scalar ratio. Using straightforward calculations, we investigate this model from the swampland conjecture perspective in terms of the cosmological parameters, i.e., ($n_s$), ($r$), and observable data such as Planck 2018, by constructing some structures such as $(c_1,2-n_s)$ and $(c_1,2-r_s)$. Then, we make a new restriction for this conjecture as $c_12c_22$ and get a limit for this model in the range $c0.0942$. We find this inflationary model is strongly in tension with the dS swampland conjecture (dSSC), i.e., $c_1=c_2 \neq \mathcal{O}(1)$. So, we shall challenge it with the FRdSSC, which has some free parameters, viz., $a,b>0$, $a+b=1$, and $q>2$. By setting these parameters, we examine the compatibility of the mentioned conjecture with this inflationary model. Finally, we infer from this string field inflation model that it satisfies the FRdSSC with the constraint of its free parameters $a$, $b$, and $q$.

hep-th↗

arXiv2022

Further Refining Swampland dS Conjecture in Mimetic f(G) Gravity

Mimetic gravity analysis has been studied as a theory in various types of general relativity extensions, such as mimetic f(R) gravity, mimetic f(R, T) gravity, mimetic f(R, G) gravity, etc., in the literature. This paper presents a set of equations arising from mimetic conditions and studies cosmic inflation with a combination of mimetic f(G) gravity and swampland dS conjectures. We analyze and evaluate these results. Therefore, we first thoroughly introduce the mimetic f(G) gravity and calculate some cosmological parameters such as the scalar spectral index, the tensor-to-scalar ratio, and the slow-roll parameters. Also, we investigate the potential according to the mimetic f(G) gravity. Then we will challenge the swampland dS conjectures with this condition. By expressing the coefficient of swampland dS conjectures viz $C_{1}$ and $C_2$ in terms of $n_{s}$ and $r$, we plot some figures and determine the allowable range for each of these cosmological parameters and these coefficients, and finally, compare these results with observable data such as Planck and BICEP2/Keck array data. We show $C_{1}$ and $C_2$ are not $\mathcal{O}(1)$, so the refining swampland dS conjecture is not satisfied for this inflationary model. Then we examine it with further refining swampland dS conjecture, which has a series of free parameters such as $a,b>0$, $q>2$, and $a+b=1$. By adjusting these parameters, the compatibility of the mentioned conjecture with the inflationary model can be discussed. We determine the further refining swampland dS conjecture is satisfied. when $a < \frac{1}{1.00489}=0.99513$, we can always find $a$, $b$ and $q$ whose value is larger than 2, viz for $q=2.4$, we find $0.99185\leq a < 1$, which we can choose $a=0.99235$ according to the condition $a < 0.99513$. Also we know $b=1-a$, so we will have $1-0.99235=0.00765 > 0$.

gr-qc↗

arXiv2022

Tsallis holographic dark energy under Complex form of Quintessence model

In this paper, we use a Tsallis holographic dark energy model in two forms, interacting and non-interacting cases, to acquire some parameters as the equation of state for the energy density of the Tsallis model in the FRW universe concerning the complex form of quintessence model. We will study the cosmology of complex quintessence by revamping the potential and investigating the scalar field dynamics. Then we analyze ($ω-ω'$) and stability in two cases, i.e., non-interacting and interacting. We will explore whether these cases describe a real universe by calculating fractional energy density $Ω_{D}$ and concerning two parts of the quintessence field effect ( complex and real part ) by considering the real part of this field to be a slow-roll field. We know that the part in which the fractional energy density ($Ω_{D} > 1$) does not describe a real universe. Also, we specified an interacting coupling parameter $b^{2}$ that depends on the constant parameter of the Tsallis holographic model ($δ$) with respect to fractional energy density ($0.73$). Unlike independence between the fractional energy density and interacting coupling in the real quintessence model, we determine a relationship among these parameters in this theory. Finally, by plotting some figures, we specify the features of ($ω-ω'$) and ($ν_{s}^{2}$) in two cases and compare the result with each other.

gr-qc↗

arXiv2022

Effects of hyperscaling violation and dynamical exponents on drag force

In this paper, we calculate the drag force of a charged particle in systems with hyperscaling violation using the AdS/CFT correspondence. We obtain energy loss, friction coefficient, diffusion and quasi normal modes of a heavy point particle. Here, we consider two cases. In the first, we assume the heavy point particle moves with constant velocity v. In the second case, we assume the heavy point particle rotates along a circle of radius L with angular velocity ω. Also, we add some electromagnetic field and obtain the energy loss. Finally, we draw some figures for the drag force with respect to the velocity and the temperature. As well, we show how the drag force and energy loss change with the hyperscaling violation parameter θ, dynamical parameter z, mass m and charge Q.

hep-th↗

arXiv2022

Effects of hyperscaling violation and dynamical exponents on heavy quark potential and jet quenching parameter

In this paper, we investigate the heavy quark potential and the jet quenching parameter in a system with Lifshitz and hyperscaling violation exponents, by using the AdS/CFT correspondence. It is shown that the heavy quark potential and the jet quenching parameter are dependent upon the nonrelativistic parameters. We show how the heavy quark potential changes with the hyperscaling violation parameter θ, dynamical parameter z, temperature T and charge Q. Increasing z and θ lead to increasing and decreasing the potential respectively. The potential decreases and increases by increasing Q and T . It is investigated how the jet quenching parameter changes with the hyperscaling violation parameter θ and dynamical parameter z. Also, we add some electromagnetic field and obtain its effect on the jet quenching parameter and see as z and θ increasing this parameter decreases and the electric and magnetic fields affect differently on that.

hep-th↗

arXiv2022

Effects of the hyperscaling violation and dynamical exponents on the imaginary potential and entropic force of heavy quarkonium via holography

The imaginary potential and entropic force are two important different mechanisms to characterize the dissociation of heavy quarkonia. In this paper, we calculate these two quantities in strongly coupled theories with anisotropic Lifshitz scaling and hyperscaling violation exponent using holographic methods. We study how the results are affected by the hyperscaling violation parameter θ and the dynamical exponent z at finite temperature and chemical potential. Also, we investigate the effect of the chemical potential on these quantities. As a result, we find that both mechanisms show the same results: the thermal width and the dissociation length decrease as the dynamical exponent and chemical potential increase or as the hyperscaling violating parameter decreases.

hep-th↗

arXiv2022

The imaginary potential and entropic force of heavy quarkonia in strongly coupled N = 4 supersymmetric Yang-Mills plasma on the Coulomb branch

There are two important different mechanisms, the imaginary potential and entropic force, to investigate the dissociation of heavy quarkonia. In this paper, we calculate these two quantities for static and moving quarkonia in the rotating black 3-brane Type IIB supergravity solution dual to N = 4 super Yang-Mills theory on the Coulomb branch (cSYM) at strong coupling. At T 6= 0, there are two black hole branches: the large and small black hole branches. We investigate the effects of rotating parameter and rapidity for the static and moving quakonium at the large and small black hole branches. We find both mechanisms have the same results. In the large black hole branch: as T/Λ and \b{eta} increase the thermal width decreases and so the suppression becomes stronger. In the small black hole branch: increasing T/Λ leads to increasing the thermal width and the quarkonium dissociates harder but \b{eta} has an opposite effect.

hep-th↗

arXiv2022

Cosmic evolution of the logarithmic f(R) model and the dS swampland conjecture

In this paper, we study the inflationary scenario in logarithmic f(R) gravity, where the rate of inflation roll is constant. On the other hand, our gravitational f(R) model is a polynomial plus a logarithmic term. We take advantage of constant-roll conditions and investigate the cosmic evolution of the logarithmic f(R) gravity. Therefore, we plot some figures such as the scalar spectrum index $n_{s}$ and tensor-to-scaler ratio $r$ concerning $n$, $β$ and model's constant parameters, i.e., $α$, $θ$ and $γ$ respectively. Also, we obtain the potential by using the constant roll condition. We know that the potential value obtained with this condition has an exact value. Next, we challenge it with refined swampland conjecture with respect to the Planck data. Finally, we compare our results with the experimental data, especially Planck 2018.

gr-qc↗

arXiv2022

The emergence of universal relations in the AdS black holes thermodynamics

Our primary goal in this paper is to confirm new universal relations in black hole thermodynamics. We investigate the universal relations by selecting different black holes. First, we obtain the black holes' thermodynamic relations assuming a new minor correction is added to the AdS part of the action. Then we confirm the universal relations by performing a series of direct calculations. It is noteworthy that according to each of the properties related to black holes, a new universal relation can be obtained according to this method. We confirm two different types of these universal relations for various block holes. Furthermore, we also consider black holes in AdS space surrounded by perfect fluid. We use the small correction to the action and obtain the modified thermodynamic quantities. We achieve two new universal relations which correspond to the parameters of perfect fluid and magnetic charge of the Bardeen AdS Black Hole. Finally, the new universal relation leads us to understand the charge-to-mass ratio, i.e., WGC-like behavior. We also find that the weak gravity conjecture condition is satisfied for the black hole surrounded by perfect fluid.

physics.gen-ph↗

arXiv2022

Swampland dS conjecture in Mimetic $f(R, T)$ gravity

In this paper, we study a theory of gravity called mimetic $f(R, T)$ in the presence of swampland dS conjecture. For this purpose, we introduce several inflation solutions of the Hubble parameter H(N) from $f(R, T)= R+δT$ gravity model, in which R is Ricci scalar, and T denotes the trace of the energy-momentum tensor. Also, $δ$ and $N$ are the free parameter and a number of e-fold, respectively. Then we calculate quantities such as potential, Lagrange multiplier, slow-roll, and some cosmological parameters such as $n_{s}$ and $r$. Then we challenge the mentioned inflationary model from the swampland dS conjecture. We discuss the stability of the model and investigate the compatibility or incompatibility of this inflationary scenario with the latest Planck observable data.

gr-qc↗

arXiv2022

Constraints on cosmological parameters in light of the scalar-tensor theory of gravity and swampland conjectures

In this paper, we study various cosmological parameters and quantities in scalar-tensor gravity from inflation and swampland conjecture. Therefore, by selecting different models such as power-law, exponential, and logarithmic in the framework of scalar-tensor theory, we obtain potential, tensor-to-scalar ratio, and the scalar spectral index. Next, we examine new constraints and compare the corresponding results with the latest observable data. Here, we take advantage of the obtained results and determine the compatibility or incompatibility of the corresponding model with the swampland conjectures

gr-qc↗

arXiv2022

Swampland conjectures in hybrid metric-Palatini gravity

In this paper, we study a hybrid combination of Einstein-Hilbert action with curvature scalar $R$, and a function $f(\mathcal{R})$ in Palatini gravity within the context of inflationary scenario, from the Swampland conjecture point of view. This hybrid model has been paid attention in recent cosmological studies, and its applications have been widely studied in the literature. In this regard, using the Swampland conjecture (using ($ C_ {1} $) as the first component of dS swampland conjecture, which is obtained from the first derivative of the potential upon the potential and ($ C_ {2} $) as the second component which is acquired from the second derivative of the potential upon the potential), we investigate the cosmological implications of the present gravity theory, with a suitable potential, in the framework of inflationary scenario to obtain cosmological quantities such as slow-roll parameter, scalar spectral index $(n_{s})$, tensor-to-scalar ratio ($r_{s}$), and then compare them with the cosmological observations. Moreover, we compare the compatibility or incompatibility of the model with observable data, such as Planck, by applying Swampland conjecture to $r_{s}-n_{s}$ , $C_{1,2}-n_{s}$ and $C_{1,2}-r_{s}$ plots.

gr-qc↗

arXiv2022

The effect of the WGC condition on the maximal energy extracted from black holes

In this paper, we study the Penrose process and the maximum energy extracted from the collision of two particles near the Kerr-Newman black hole with WGC condition. We consider the collision process when two particles collide in the ergosphere region of a black hole, scattering two new particles; one of them falls into the black hole and the other escapes to infinity. Our calculations also show an increasing in the energy. We also checked how much energy could be received from a black hole for particles with different spins. Results of this paper will help us to identify and study the black holes of astrophysics and the particles with different spins. Also, it states how black holes work in WGC conditions.

gr-qc↗