arXiv subjects

Hassan Hassanabadi

Publications and source records attributed to Hassan Hassanabadi.

At least 37 records · Page 2Linked to original sources

arXiv2026

Charged particle dynamics in singular spacetimes: hydrogenic mapping and curvature-corrected thermodynamics

We analyze the dynamics of charged test particles in a singular, horizonless spacetime arising as the massless limit of a charged wormhole in the Einstein--Maxwell--Scalar (EMS) framework. The geometry, sustained solely by an electric charge $Q$, features an infinite sequence of curvature singularity shells, with the outermost at $ r_* = \frac{2|Q|}π $ acting as a hard boundary for nonradial motion, while radial trajectories can access it depending on the particle charge-to-mass ratio $ |q|/m $. Exploiting exact first integrals, we construct the effective potential and obtain circular orbit radii, radial epicyclic frequencies, and azimuthal precession rates. In the weak-field limit ($ r \gg |Q| $), the motion reduces to a Coulombic system with small curvature-induced retrograde precession. At large radii, the dynamics maps to a hydrogenic system, with curvature corrections inducing perturbative energy shifts. Approaching $ r_* $, the potential diverges, producing hard-wall confinement. Curvature corrections also modify the spectral thermodynamics, raising energies and slightly altering entropy and heat capacity. Our results characterize the transition from Newtonian-like orbits to strongly confined, curvature-dominated dynamics.

gr-qc↗

arXiv2025

Novel topological subclass in Hourava-Lifshitz black holes

This work explores the universal classification of thermodynamic topology for charged static black holes within the $z=3$ Hourava-Lifshitz gravity theory, considering both canonical and grand canonical ensembles. We introduce a new topological subclass, denoted as $\ddot{W}^{1-}$. This finding expands the existing topological classification, going beyond the five previously defined classes and their respective subclasses. The $\ddot{W}^{1-}$ subclass presents a distinct and previously unobserved stability profile: In the low-temperature regime, an unstable small black hole appears in the phase space, whereas, while in the high temperature regime, two unstable small black holes exist together with a stable large black hole. Our study underscores the dependence of charged black hole stability on the selection of the ensemble. These results contribute to refining and expanding the topological framework in black hole thermodynamics, providing key perspectives on the underlying nature of black holes and gravity.

gr-qc↗

arXiv2025

Universal topological classes of black holes surrounded by quintessence

This work explores the universal topological classes of various black hole configurations immersed in a quintessence field. The results indicate that the Schwarzschild black hole surrounded by quintessence is of the $W^{1-}$ type, exhibiting thermodynamic instability in both extremal temperature limits. The introduction of rotation alters its topological nature to the $W^{0+}$ class, where the Kerr black hole displays coexistence of a stable small black hole and an unstable large black hole at low temperatures. In comparison, anti de Sitter (adS) black holes display different thermodynamic topologies. The Schwarzschild-adS solution corresponds to the $W^{0-}$ class, where an unstable small branch and a stable large branch emerge in the high temperatures. Meanwhile, the Kerr-adS classified as $W^{1+}$, maintains stability in both high- and low-temperature limits. Furthermore, the 4D/5D quintessential black hole belongs to the $W^{0+}$ class within the Einstein-Gauss-Bonnet framework. Overall, parameters such as rotation and Gauss-Bonnet in quintessence background field affect the topological classifications of the black holes, while the quintessence field primarily modifies the stability range without changing the topological class itself.

gr-qc↗

arXiv2025

Accretion Disk Luminosity and Topological Characteristics for a Schwarzschild Black Hole Surrounded by King Dark Matter Halo

This study delves into the intricate properties of a Schwarzschild black hole enveloped by King dark matter in an isotropic configuration. The thermodynamic characteristics of this black hole are meticulously analyzed, and the dynamics of massive and massless particles in its vicinity are investigated. In examining the trajectories of massless particles, the shadow cast in the presence of King dark matter is explored, revealing virtual ranges for the corresponding parameters. For the dynamics of massive particles, the radius of the innermost stable circular orbit, angular momentum, energy, and angular velocity of a test particle within the King dark matter framework surrounding the black hole are calculated. The effect of King dark matter on the accretion disk energy flux, effective radiation temperature, differential luminosity, and spectral luminosity are then investigated. The stability of the photon sphere in the presence of King dark matter is also studied, and finally, the thermodynamic potentials of this black hole are examined from a topological perspective.

gr-qc↗

arXiv2025

Probing regular black holes with sub-Planckian curvature through periodic orbits and their gravitational wave radiation

Extreme mass-ratio inspirals (EMRIs) are among the key targets for future space-based gravitational wave detectors. The gravitational waveforms emitted by EMRIs are highly sensitive to the orbital dynamics of the small compact object, which in turn are determined by the geometry of the underlying spacetime. In this paper, we explore the de- tectability of regular black holes with sub-Planckian curvature, which can be interpreted as regularized versions of the Schwarzschild black hole (RSBH). To do so, we begin by ana- lyzing the metric and geodesics, determining the effective potential, and investigating the marginally bound orbits and the innermost stable circular orbits for timelike particles. Our analysis reveals that orbital radius, angular momentum, and energy significantly depend on the model parameter α for both orbits. Our main aim is to focus on the influence of the model parameter on a specific kind of orbit, the periodic orbit, surrounding a supermassive RSBH. The findings show that, for a constant rational integer, α has a significant impact on the energy and angular momentum of the periodic orbit. Utilising the numerical kludge method, we further investigate the gravitational waveforms of the small celestial body over various periodic orbits. The waveforms display discrete zoom and spin phases within a complete orbital period, influenced by the RSBH parameter α. As the system evolves, the phase shift in the gravitational waveforms grows progressively more pronounced, with cumulative deviations amplifying over time. With the ongoing advancements in space- based gravitational wave detection systems, our results will aid in leveraging EMRIs to probe and characterize the RSBH properties.

gr-qc↗

arXiv2025

Thermodynamics of the Reissner-Nordström black hole with quintessence matter on the EGUP framework

In this paper, we investigate the quantum correction on thermodynamics of the Reissner-Nordström black hole in the presence of the quintessence matter associated with dark energy. To this end, the modified Hawking temperature, heat capacity, and entropy functions of the black hole are derived. { Investigation reveals that the modified uncertainty principles and normalization factor $α$ restrict the lower bound value of horizon radius to affect the Hawking temperature and the parameter $η_{0}$ have a non-negligible effect on the heat capacity threshold.} {Furthermore}, the correction of entropy does not depend on the quintessence matter. It is also examined the equation of state associated with the pressure and the volume in this framework. In addition, we employ graphical methods to compare and discuss the findings within the generalized uncertainty principle (GUP) and extended uncertainty principle (EUP).

gr-qc↗

arXiv2025

Universal thermodynamic topological classes of static black holes in Conformal Killing Gravity

In this study, we develop universal thermodynamic topological classes for the static black holes in the context of the Conformal Killing Gravity. Our findings indicate that the Conformal Killing Gravity significantly reconstructs the thermodynamic properties of both the smallest inner and the largest outer black hole states. Additionally, it considerably alters the thermodynamic stability of black holes across both high-temperature and low-temperature regimes. This analysis shows that different CKG parameter settings will lead to $W^{0+}$ $(λ>0)$ and $W^{1+}$ $(λ<0)$ categories for the charged AdS black hole, the Reissner-Nordstr$\ddot{o}$m black hole in Conformal Killing Gravity is classified into the $W^{0+}$ and $W^{1+}$ categories. Furthermore, we examine the specific scenario where charge is neglected. The study reveals that within the framework of Conformal Killing Gravity, the Schwarzschild black hole similar to the Schwarzschild-AdS black hole, can be classified into the $W^{1-}$ and $W^{0-}$ categories. This work provides key insights into the fundamental nature of quantum gravity theory.

gr-qc↗

arXiv2025

Quasinormal Modes and Topological Characteristics of a Schwarzschild Black Hole Surrounded by the Dehnen Type Dark Matter Halo

In this work, we explore the critical parameters that delineate the existence of black holes, identifying the permissible ranges that facilitate their formation. A comprehensive thermodynamic analysis of black holes is conducted, leading to the calculation of black hole remnants. We investigate the trajectory of light, establishing an upper limit for the parameters based on Event Horizon Telescope (EHT) observations of Sgr A*, ensuring that the black hole's shadow resides within the allowed region. Furthermore, we derive the quasinormal modes (QNMs) for both scalar and electromagnetic perturbations. Utilizing a topological framework, we examine the stability of the photon sphere and classify the topology of the black hole in accordance with its thermodynamic potentials.

gr-qc↗

arXiv2025

Optics in spiral dislocation spacetime: Torsion as a geometric waveguide and frequency-filtering mechanism

We present an exact analytical investigation of null trajectories and scalar wave propagation in a $(2+1)$-dimensional spacetime containing a spiral dislocation-a topological defect characterized by torsion in the absence of curvature. For null rays, the torsion parameter $β$ modifies the affine structure, enforcing a finite turning radius $r_{\min} = \sqrt{b^2 - β^2}$ and inducing a torsion-mediated angular deflection that decreases monotonically with increasing $β$. The photon trajectory deviates from the curvature-induced lensing paradigm, exhibiting a purely topological exclusion zone around the defect core. In the wave regime, we recast the Helmholtz equation into a Schrödinger-like form and extract a spatially and spectrally dependent refractive index $n^2(r,k)$. This index asymptotically approaches unity at large distances, but diverges strongly and negatively near the dislocation core due to torsion-induced geometric terms. The resulting refractive index profile governs the transition from propagating to evanescent wave behavior, with low-frequency modes experiencing pronounced localization and suppression. Our findings reveal that torsion alone, absent any curvature, can act as a geometric regulator of both classical and quantum propagation, inducing effective anisotropy, frequency filtering, and confinement. This framework provides a rare exact realization of light-matter interaction in a torsion-dominated background, with potential applications in analog gravity systems and photonic metamaterials engineered to replicate non-Riemannian geometries.

gr-qc↗

arXiv2025

Accretion Disk Luminosity and Topological Characteristics for a Schwarzschild Black Hole Surrounded by a Hernquist Dark Matter Halo

In this work, we study some characteristics and gravitational signatures of the Schwarzschild black hole immersed in a Hernquist dark matter halo (SBH-HDM). We determine the black hole's remnant radius and mass, which provide useful residual information at the end of its evaporation. We then explore the luminosity of the accretion disk from the SBH-HDM model. In this way, we determine the key orbital parameters of the test particles within the accretion disk, such as angular velocity, angular momentum, energy, and the radius of the innermost stable circular orbit, based on the dark matter model parameters. We also numerically estimate the accretion disk's efficiency in converting matter into radiation. We also demonstrate that dark matter, which significantly alters the geometry surrounding a Schwarzschild black hole, influences the accretion disk's radiative flux, temperature, differential luminosity, and spectral luminosity. The stability of a black hole spacetime is determined in the eikonal regime. The Lyapunov exponent is also analyzed to quantify the stability of the particle regime and to demonstrate the infall into or escape from the black hole to infinity, as well as the quasi-normal modes. Finally, some properties of black holes are studied from a topological perspective.

gr-qc↗

arXiv2025

Spiral dislocation as a tunable geometric parameter for optical responses in quantum rings

We investigate the optical and quantum mechanical properties of a charged spinless particle confined in a two-dimensional quantum ring under the simultaneous influence of a spiral dislocation and an external magnetic field. The dislocation is modeled by a torsion-induced metric that alters the spatial geometry without introducing curvature. Using the minimal coupling procedure in curved space, we derive a modified Schrödinger equation incorporating both topological and electromagnetic effects. The geometric deformation leads to an energy-dependent effective potential, enabling a tunable control over the bound-state spectrum. We analyze how the spiral dislocation modifies the absorption coefficient, refractive index variation, and photoionization cross-section. The results demonstrate that the dislocation not only shifts the resonance peaks but also enhances or suppresses specific optical transitions depending on the angular momentum. These findings open up possibilities for geometrically tuning light-matter interactions in topological quantum devices.

cond-mat.mes-hall↗

arXiv2025

Modified Kerr black holes surrounded by dark matter spike

We study supermassive black holes (SMBH), surrounded by a dark matter (DM) spike, that can be found at the centers of Milky Way and $\text{M87}$ galaxies and are accompanied by a specific kind of topological defect. The investigation is developed within the framework of Bumblebee Gravity with a global monopole (BGGM). The dark matter spike is described by a power-law density profile. Our main objective is to assess how the background arising from spontaneous Lorentz symmetry breaking and the presence of a global monopole influence the properties of the Kerr BH within the region affected by the spike. Using a spherically symmetric static BH with BGGM properties as the seed metric, we construct a non-rotating spacetime with a DM spike, resulting in a BGGM-motivated Schwarzschild-like BH by solving the modified Tolman-Oppenheimer-Volkoff equations (TOV). Next, we extend this approach to the case of a rotating spacetime resulting in the BGGM-motivated Kerr-like BH (BGMKLBH). This approach allows us to explore the spacetime structure, and the BGMKLBH shadows. Then, using available observational data for the DM spike density and considering the effects of BGGM on $\text{Sgr A}^{*}$ and $\text{M87}^{*}$ SMBHs, we analyse the shapes of their shadows and put constraints on the BGGM parameter. Thus, we infer that the BGMKLBHs could be reliable candidates for the astrophysical BHs.

gr-qc↗

arXiv2025

Two types of $q$-Gaussian distributions used to study the diffusion in a finite region

In this work, we explore both the ordinary $q$-Gaussian distribution and a new one defined here, determining both their mean and variance, and we use them to construct solutions of the $q$-deformed diffusion differential equation. This approach allows us to realize that the standard deviation of the distribution must be a function of time. In one case, we derive a linear Fokker-Planck equation within a finite region, revealing a new form of both the position- and time-dependent diffusion coefficient and the corresponding continuity equation. It is noteworthy that, in both cases, the conventional result is obtained when $q$ tends to zero. Furthermore, we derive the deformed diffusion-decay equation in a finite region, also determining the position- and time-dependent decay coefficient. A discrete version of this diffusion-decay equation is addressed, in which the discrete times have a uniform interval, while for the discrete positions the interval is not uniform.

cond-mat.stat-mech↗

arXiv2025

A new time-dependent quantum theory based on Tsallis' distribution

In this paper, inspired by Tsallis' probability distribution based on a $q$-deformed Boltzmann factor, we stipulate a new $q$-deformed quantum dynamics by applying the inverse Wick rotation $ β\rightarrow i t$ to the Tsallis-deformed Boltzmann factor. We obtain a new time-dependent $q$-deformed Schrödinger equation. The free time-evolution of a Gaussian wave packet and that induced by an harmonic interaction are studied within this $q$-deformed quantum mechanical framework.

quant-ph↗

arXiv2025

An algebraic approach to gravitational quantum mechanics

Most approaches towards a quantum theory of gravitation indicate the existence of a minimal length scale of the order of the Planck length. Quantum mechanical models incorporating such an intrinsic length scale call for a deformation of Heisenberg's algebra resulting in a generalized uncertainty principle and constitute what is called gravitational quantum mechanics. Utilizing the position representation of this deformed algebra, we study various models of gravitational quantum mechanics. The free time evolution of a Gaussian wave packet is investigated as well as the spectral properties of a particle bound by an external attractive potential. Here the cases of a box with infinite walls and an attractive potential well of finite depth are considered.

gr-qc↗

arXiv2024

Thermodynamic topology of Phantom AdS Black Holes in Massive Gravity

In this work, we explore the thermodynamic topology of phantom AdS black holes in the context of massive gravity. To this end, we evaluate these black holes in two distinct ensembles: the canonical and grand canonical ensembles (GCE). We begin by examining the topological charge linked to the critical point and confirming the existence of a conventional critical point $(CP_{1})$ in the canonical ensemble (CE), this critical point has a topological charge of $-1$ and acts as a point of phase annihilation, this situation can only be considered within the context of the classical Einstein-Maxwell (CEM) theory $(η=1)$, while no critical point is identified in the GCE. Furthermore, we consider black holes as a topological defect within the thermodynamic space. To gain an understanding of the local and global topological configuration of this defect, we will analyze its winding numbers, and observe that the total topological charge in the CE consistently remains at $1$. When the system experiences a pressure below the critical threshold, it gives rise to the occurrence of annihilation and generation points. The value of electric potential determines whether the total topological charge in the GCE is zero or one. As a result, we detect a point of generation point or absence of generation/annihilation point. Based on our analysis, it can be inferred that ensembles significantly impact the topological class of phantom AdS black holes in massive gravity.

gr-qc↗

arXiv2024

Thermodynamic topology of Kerr-Sen black holes via Rényi statistics

In the present study, we investigate the topological properties of black holes in terms of Rényi statistics as an extension of the Gibbs-Boltzmann (GB) statistics, aiming to characterize the non-Boltzmannian thermodynamic topology of Kerr-Sen and dyonic Kerr-Sen black holes. Through this research, we discover that the topological number derived via Rényi statistics differs from that obtained through GB statistics. Interestingly, although the non-extended parameter $λ$ changes the topological number, the topological classification of the Kerr-Sen and dyonic Kerr-Sen black holes remains consistent under both GB and Rényi statistics. In addition, the topological numbers associated with these two types of black holes without cosmological constant using Rényi entropy processes are the same as the AdS cases of them by considering the GB entropy, as further evidenced by such a study found here. This indicates the cosmological constant has some potential connections the with the nonextensive Rényi parameter from the perspective of thermodynamic topology.

gr-qc↗

arXiv2024

Shadows, rings and optical appearance of a magnetically charged regular black hole illuminated by various accretion disks

The Event Horizon Telescope (EHT) imaging of the supermassive black holes at the centers of Messier 87 galaxy and the Milky Way galaxy marks a significant step in observing the photon rings and central brightness depression that define the optical appearance of black holes with an accretion disk scenario. Inspired by this, we take into account a static and spherically symmetric magnetically charged regular black hole (MCRBH) metric characterized by its mass and an additional parameter q, which arises from the coupling of Einstein gravity and nonlinear electrodynamics (NLED) in the weak field approximation. This parameterized model offers a robust foundation for testing the coupling of Einstein gravity and NLED in the weak-field approximation, using the EHT observational results. In this study, we investigate the geodesic motion of particles around the solution, followed by a discussion of its fundamental geometrical characteristics such as scalar invariants. Using null geodesics, we examine how the model parameter influences the behavior of the photon sphere radius and the associated shadow silhouette. We seek constraints on q by applying the EHT results for supermassive black holes M87* and Sgr A*. Furthermore, it is observed that the geodesics of time-like particles are susceptible to variations in q, which can have an impact on the traits of the innermost stable circular orbit and the marginally bounded orbit. Our primary objective is to probe how the free parameter q affects various aspects of the accretion disk surrounding the MCRBH using the thin-disk approximation. Next, we discuss the physical characteristics of the thin accretion disk as well as the observed shadows and rings of the MCRBH, along with its luminosity, across various accretion models. Ultimately, variations in accretion models and the parameter q yield distinct shadow images and optical appearances of the MCRBH.

astro-ph.HE↗