arXiv subjects

S. Zare

Publications and source records attributed to S. Zare.

At least 19 recordsLinked to original sources

arXiv2026

Constrained thermodynamics and geodesic observables of an effective non-commutative Kerr-like black hole

We investigate the horizon structure, constrained thermodynamics, and geodesic properties of an effective Kerr-like black hole in a non-commutative background. Deformation modifies the radial geometry through a mass-dependent charge-like contribution, while preserving the separability of the geodesic equations. We determine the conditions for horizon existence, identify the extremal zero-temperature configuration, and analyze the stationary-limit surfaces and the ergoregion. Special attention is paid to the thermodynamic interpretation of the model, where the geometric Hawking quantities are distinguished from the conjugate variables associated with the constrained state space at fixed non-commutative deformation parameter. The canonical and grand-canonical heat capacities are derived to characterize their ensemble-dependent local thermal behavior. We also obtain the spherical photon region, equatorial light rings, and shadow boundary, showing that the deformation shifts the characteristic photon orbits inwards and reduces the overall size of the shadow. Timelike circular motion is studied through the innermost stable circular orbit, where non-commutative correction produces an inward shift of both the prograde and retrograde branches. Finally, invariant photon frequency shifts are obtained by treating the emitter's orbital direction and the photon's tangential emission direction as independent physical choices.

gr-qc↗

arXiv2026

GUP-corrected black holes: Thermodynamic properties, evaporation time and shadow constraint from EHT Observations of M87* and Sgr A*

In this manuscript, we implement the generalized uncertainty principle (GUP) with linear and quadratic moment for Schwarzschild black hole metric in order to study the influence of quantum effect on the thermodynamics and evaporation of black hole. To this end, we first derive the GUP-modified Hawking temperature of a black hole in the semi-classical framework. Due to the existence of the GUP effect, there is a maximum Hawking temperature. We determine the entropy, heat capacity and Helmholtz free energy with heuristic analysis that investigates the particle absorbed by black hole. Furthermore, we also verify that these quantities are modified by the GUP, the influence of quantum effect on the black hole phase transition is discussed in detail. Then, we analyze the black hole evaporation process in the mentioned framework and examine the obtained results by graphical methods and compare them with each other. We likewise explore the behavior of the event horizon radius, photon sphere radius, and shadow silhouette when influenced by the GUP-corrected Schwarzschild black hole (GCSBH) parameters. We intend to establish restrictions for $\alpha$ by utilizing the event horizon telescope (EHT) data for M87* and Sagittarius A* (Sgr A*). Our findings show that Sgr A* provides more robust constraints. As the parameter $\beta$ grows, the range of constraints for $\alpha$ expands. For Sgr A* one, we find that the shadow radius is close to the observed value at smaller values of $\alpha$.

gr-qc↗

arXiv2025

Ergosphere Dynamics and Rotational Energy Extraction in Bumblebee Kerr-Newman-AdS Black Holes

We present a comprehensive analysis of the thermodynamic and optical properties of the Bumblebee Kerr-Newman-Anti-de Sitter (AdS) black hole, a rotating and charged configuration arising in Lorentz symmetry-violating (LSV) gravity. The influence of the black hole parameters on the horizon structure, thermodynamic stability, and geometric deformation of spacetime is systematically investigated. Explicit expressions for the Hawking temperature, entropy, and heat capacity are derived, revealing the formation of black hole remnants and extended stability phases induced by Lorentz symmetry-violating (LSV) effects. The sparsity of Hawking radiation is quantified, showing that Lorentz violation suppresses the continuum limit and produces a more discrete, less thermal emission spectrum. A detailed analysis of null geodesics is performed to determine the photon region and shadow morphology, indicating that increasing l and Q compresses and distorts the shadow boundary, while rotation diminishes its overall size. The ergosphere geometry is analyzed in detail, showing that increases in a, l, and Q not only enlarge and distort the ergoregion but also intensify frame-dragging, thereby maximizing the efficiency of energy extraction via the Penrose process. These results reveal clear and potentially observable deviations from standard Kerr-Newman-AdS predictions, providing a powerful new avenue to probe Lorentz symmetry breaking and test the fundamental structure of gravity in extreme strong field regimes.

gr-qc↗

arXiv2025

Black holes immersed in polytropic scalar field gas

By implementing the concept of polytropic structures as a scalar field gas with a dark energy-like behavior, we obtain a static spherically symmetric black hole solution in the framework of general relativity. In this paper, we study the quasinormal modes, the greybody bound process, the shadow behaviors, and the sparsity of black holes with a surrounding polytropic scalar field gas. Using the Wentzel-Kramers-Brillouin approach, we evaluate the impact of a particular set of polytropic parameters $(\xi, A)$ with a fixed setting of the polytropic index $n$ on the oscillation frequency and damping rate of gravitational waves. The results show that the effect of the parameter $\xi$ is much less significant than that of the parameter $A$ on the gravitational waves oscillation frequency and damping rate. Furthermore, the analysis of the greybody factor bounds reveals special insight into the effect of certain parameters where the multipole moments $l$ and the polytropic index $n$ have similar effects, in contrast to the pair of polytropic parameters ($\xi,A$). On the other hand, exploring the sparsity of Hawking radiation is another task that provides a better understanding of the behaviour of the black hole solution. In this respect, the results show that the black hole behaves like blackbody radiation for a sufficiently large entropy. And for $\xi=A=0$, the relevant sparsity acts exactly like the Schwarzschild sparsity. These results provide an insight into the dynamics of black holes with a surrounding polytropic scalar field gas from the analysis of their quasinormal modes, greybody factors, shadow behaviors, energy emission rate and sparsity process. Constraints on the associated BH parameters, derived from the Event Horizon Telescope observations of M87* and Sgr A*, indicate that this black hole model stands as a compelling candidate for representing astrophysical black holes.

gr-qc↗

arXiv2024

Influences of modified Chaplygin dark fluid around a black hole

In this work, we study a static, spherically charged AdS black hole within a modified cosmological Chaplygin gas (MCG), adhering to the calorific equation of state, as a unified dark fluid model of dark energy and dark matter. We explore the influence of model parameters on several characteristics of the MCG-motivated charged AdS black hole (MCG-AdSBH), including the geodesic structure and some astrophysical phenomena such as null trajectories, shadow silhouettes, light deflection angles, and the determination of greybody bounds. We then discuss how the model parameters affect the Hawking temperature, remnant radius, and evaporation process of the MCG-AdSBH. Quasinormal modes are also investigated using the eikonal approximation method. Constraints on the MCG-AdSBH parameters are derived from EHT observations of M87* and Sgr A*, suggesting that MCG-AdSBH could be strong candidates for astrophysical black hole.

astro-ph.HE↗

arXiv2024

Accelerating AdS black holes in gravity's rainbow

Motivated by the effect of the energy of moving particles in $C-$metric, we first obtain exact accelerating black hole solutions in gravity's rainbow. Then, we study the effects of gravity's rainbow and $C-$metric parameters on the Ricci and Kretschmann scalars, and also the asymptotical behavior of this solution. Next, we indicate how different parameters of the obtained accelerating black holes in gravity's rainbow affect thermodynamics quantities (such as the Hawking temperature, and entropy) and the local stability (by evaluating the heat capacity). In the following, we extract the geodesic equations to determine the effects of various parameters on photon trajectory in the vicinity of this black hole, as well as obtain the radius of the photon sphere and the corresponding critical impact parameter to gain insight into AdS black hole physics by adding the gravity's rainbow to $C-$metric.

gr-qc↗

arXiv2023

Gravitational traces of bumblebee gravity in metric-affine formalism

This work explores various manifestations of bumblebee gravity within the metric-affine formalism. We investigate the impact of the Lorentz violation parameter, denoted as $X$, on the modification of the Hawking temperature. Our calculations reveal that as $X$ increases, the values of the Hawking temperature attenuate. To examine the behavior of massless scalar perturbations, specifically the quasinormal modes, we employ the WKB method. The transmission and reflection coefficients are determined through our calculations. The outcomes indicate that a stronger Lorentz-violating parameter results in slower damping oscillations of gravitational waves. To comprehend the influence of the quasinormal spectrum on time-dependent scattering phenomena, we present a detailed analysis of scalar perturbations in the time-domain solution. Additionally, we conduct an investigation on shadows, revealing that larger values of $X$ correspond to larger shadow radii. Furthermore, we constrain the magnitude of the shadow radii using the EHT horizon-scale image of $Sgr A^*$. Finally, we calculate both the time delay and the deflection angle.

gr-qc↗

arXiv2023

Gravitational signatures of a non--commutative stable black hole

This work investigates several key aspects of a non--commutative theory with mass deformation. We calculate thermodynamic properties of the system and compare our results with recent literature. We examine the \textit{quasinormal} modes of massless scalar perturbations using two approaches: the WKB approximation and the P\"oschl--Teller fitting method. Our results indicate that stronger non--commutative parameters lead to slower damping oscillations of gravitational waves and higher partial absorption cross sections. Furthermore, we study the geodesics of massless and massive particles, highlighting that the non--commutative parameter $\Theta$ significantly impacts the paths of light and event horizons. Also, we calculate the shadows, which show that larger values of $\Theta$ correspond to larger shadow radii, and provide some constraints on $\Theta$ applying the observation of Sgr $A^{*}$ from the Event Horizon Telescope. Finally, we explore the deflection angle in this context.

gr-qc↗

arXiv2023

Dark matter spike around Bumblebee black holes

The effects of dark matter spike in the vicinity of the supermassive black hole, located at the center of M87 (the Virgo A galaxy), are investigated within the framework of the so-called Bumblebee Gravity. Our primary aim is to determine whether the background of spontaneous Lorentz symmetry breaking has a significant effect on the horizon, ergo-region, and shadow of the Kerr Bumblebee black hole in the spike region. For this purpose, we first incorporate the dark matter distribution in a Lorentz-violating spherically symmetric space-time as a component of the energy-momentum tensors in the Einstein field equations. This leads to a space-time metric for a Schwarzschild Bumblebee black hole with a dark matter distribution in the spike region and beyond. Subsequently, this solution is generalized to a Kerr Bumblebee black hole through the use of the Newman-Janis-Azreg-A\"inou algorithm. Then, according to the available observational data for the dark matter spike density and radius, and the Schwarzschild radius of the supermassive black hole in Virgo A galaxy, we examine the shapes of shadow and demonstrate the influence of the spin parameter $a$, the Lorentz-violating parameter $\ell$ and the corresponding dark matter halo parameters $\rho_{0}$ and $r_{0}$ on the deformation and size of the shadow.

gr-qc↗

arXiv2022

Thermodynamics and evaporation of a modified Schwarzschild black hole in a non--commutative gauge theory

In this work, we study the thermodynamic properties on a non--commutative background via gravitational gauge field potentials. This procedure is accomplished after contracting de Sitter (dS) group, $\mathrm{SO}(4,1)$, with the Poincar\`e group, $\mathrm{ISO}(3,1)$. Particularly, we focus on a static spherically symmetric black hole. In this manner, we calculate the modified Hawking temperature and the other deformed thermal state quantities, namely, entropy, heat capacity, Helmholtz free energy and pressure. Finally, we also investigate the black hole evaporation process in such a context.

hep-th↗

arXiv2021

Duffin-Kemmer-Petiau particles in the presence of the spiral dislocation

In this study, we investigated the influence of the topological defects space-time with a spiral dislocation on a spin-zero boson field by using the Duffin-Kemmer-Petiau (DKP) equation. To be more specific, we solved the generalized spin-zero DKP equation in the presence of a spiral dislocation exactly. We derived the wave function and corresponding energy eigenvalues for two cases, in the absence and presence of a static potential by using analytical methods. We numerically demonstrated the effect of the spiral dislocation on the solutions.

hep-th↗

arXiv2021

Interaction of the magnetic quadrupole moment of a non-relativistic particle with an electric field in the background of screw dislocations with a rotating frame

In this study, we considered a moving particle with a magnetic quadrupole moment in an elastic medium in the presence of a screw dislocation. We assumed a radial electric field in a rotating frame that leads a uniform effective magnetic field perpendicular to the plane of motion. We solved the Schrödinger equation to derive wave and energy eigenvalue functions by employing analytical methods for two interaction configurations: in the absence of potential and in the presence of a static scalar potential. Due to the topological defect in the medium, we observed a shift in the angular momentum quantum number which affects the energy eigenvalues and the wave function of the system.

quant-ph↗

arXiv2021

Electric quadrupole moment of a neutral non-relativistic particle in the presence of screw dislocation

In this contribution, we investigate the interaction between electric and magnetic fields with an electric quadrupole moment of a spinless particle moving in an elastic medium which has a topological defect (screw dislocation). By considering this interaction, the Schrödinger equation is exactly solved by using the analytical method. Thus, the eigenfunction and energy eigenvalues for two configurations are found. Meanwhile, by observing a shift in the angular momentum quantum number, the energy eigenvalues and the wave function of the system are modified, due to the screw dislocation in the medium.

quant-ph↗

arXiv2019

Well-indumatched Trees and Graphs of Bounded Girth

A graph G is called well-indumatched if all of its maximal induced matchings have the same size. In this paper we characterize all well-indumatched trees. We provide a linear time algorithm to decide if a tree is well-indumatched or not. Then, we characterize minimal well-indumatched graphs of girth at least 9 and show subsequently that for an odd integer g greater than or equal to 9 and different from 11, there is no well-indumatched graph of girth g. On the other hand, there are infinitely many well-indumatched unicyclic graphs of girth k, where k is in {3, 5, 7} or k is an even integer greater than 2. We also show that, although the recognition of well-indumatched graphs is known to be co-NP-complete in general, one can recognize in polynomial time well-indumatched graphs where the size of maximal induced matchings is fixed.

cs.DM↗

arXiv2017

Klein-Gordon equation particles in exponential-type molecule potentials and its thermodynamic properties in D- dimensions

In this paper we use the Nikiforv-Uvarov method to obtain the approximate solutions of the Klein-Gordon equation with deformed five parameter exponential type potential (DFPEP) model. We also obtain the solutions of the Schrödinger equation in the presence of the DFPEP in the non-relativistic limits. In addition, we calculate in the nonrelativistic limits the thermodynamics properties such as vibrational mean energy U, free energy F and the specific heat capacity C . Special cases of the potential are also discussed.

quant-ph↗

arXiv2016

Scattering states of Dirac particle equation with position dependent mass under the cusp potential

We solved the one-dimensional position-dependent mass Dirac equation in the presence of the cusp potential and reported the solutions in terms of the Whittaker functions. We have derived the reflection and transmission coefficients by making use of the matching conditions on the wave functions. The effect of position dependent mass on the reflection and transmission coefficients of the system is duly investigated.

nucl-th↗

arXiv2016

Scattering states of position-dependent mass Schrödinger equation with non central potential

In this paper, we study the time-independent Schrödinger equation within the formalism of position dependent effective mass. For a generalized decomposition of the non-central effective potential, the deformed Schrödinger equation can be easily solved analytically through separation of variables. The energy eigenvalues and the normalization constant of the radial wave functions are obtained, as well as the scattering phase shifts.

quant-ph↗

arXiv2015

On 1-sum flows in undirected graphs

Let G=(V,E) be a simple undirected graph. For a given set L of the real line, a function omega from E to L is called an L-flow. Given a vector gamma whose coordinates are indexed by V, we say that omega is a gamma-L-flow if for each v in V, the sum of the values on the edges incident to v is gamma(v). If gamma(v)=c, for all v in V, then the gamma-L-flow is called a c-sum L-flow. In this paper we study the existence of gamma-L-flows for various choices of sets L of real numbers, with an emphasis on 1-sum flows. Given a natural k number, a c-sum k-flow is a c-sum flow with values from the set {-1,1,...,1-k, k-1}. Let L be a subset of real numbers containing 0 and let L* be L minus 0 by L*. Answering a question from a recent paper we characterize which bipartite graphs admit a 1-sum R*-flow or a 1-sum Z*-flow. We also show that that every k-regular graph, with k either odd or congruent to 2 modulo 4, admits a 1-sum {-1, 0, 1}-flow.

math.CO↗