arXiv subjects

Karima Masmar

Publications and source records attributed to Karima Masmar.

5 recordsLinked to original sources

arXiv2026

QPO-Based Bayesian Constraints on Charged Particle Dynamics Around Magnetized Schwarzschild Black Holes

We study the motion of charged particles with a magnetic dipole moment orbiting a Schwarzschild black hole immersed in an external paraboloidal magnetic field. The interaction between the particle's intrinsic magnetic moment and the black hole magnetosphere is modeled through a dipole coupling, and the equations of motion are derived using the Hamilton-Jacobi formalism. We analyze equatorial circular orbits, the innermost stable circular orbit, and epicyclic oscillations, showing that the magnetic field strength and coupling parameter produce competing effects on orbital stability and fundamental frequencies. These frequencies are applied to model high-frequency quasi-periodic oscillations within the relativistic precession framework. Using observational QPO data from stellar-mass, intermediate-mass, and supermassive black holes, we perform a Bayesian parameter estimation based on Markov Chain Monte Carlo techniques. The analysis constrains the black hole mass, magnetic field strength, field geometry, coupling parameter, and QPO orbital radius, highlighting the role of magnetospheric interactions in shaping both particle dynamics and timing properties of accreting black holes.

gr-qc↗

arXiv2025

Modeling HF-QPOs in Microquasars and AGNs: Charged Particles around Black Holes with CDM Halos

HF QPOs are among the most intriguing phenomena observed in LMXBs containing BHs or neutron stars. In this work, we investigate charged particles' dynamics in the nearby of a Schwarzschild-like BH embedded in a uniform magnetic field and surrounded on all sides by CDM. Thereby, gaining deeper insight into the influence of magnetic and DM distributions on observable phenomena near compact objects. We first present a modified metric, which incorporates the effects of a CDM, and we explore how both DM and magnetic fields influence the effective potential, stable circular orbits, and escape conditions for ionized particles. Employing a Hamiltonian formalism, we analyze the energy boundaries and ISCO, demonstrating that CDM causes an outward shift of the ISCO, while magnetic fields tend to pull it closer to the event horizon. We compute the fundamental oscillation frequencies-radial, latitudinal, Keplerian, and Larmor-and demonstrate how their variation depends on the combined influence of CDM and magnetic field strength. The resulting frequency structure allows us to identify resonance radii associated with HF QPOs, particularly those in 3:2 ratios observed in microquasars. We assess several theoretical models for QPO generation, including the ...... Our results highlight the importance of including both magnetic and dark matter (DM) effects in strong-field astrophysics and support the use of HF QPOs as sensitive probes of BH environments. This study opens new perspectives for exploring particle dynamics, accretion disk structure, and observational signatures of DM near compact objects.

astro-ph.HE↗

arXiv2023

Topology of Born-Infeld-AdS Black Hole Phase Transitions: Bulk and CFT Sides

The thermodynamic criticality of the AdS black holes serves as an important structure during the thermal phase transition. This paper discusses about the critical points and their topology during thermal phase transitions of the Born-Infeld AdS black holes. We make such investigations using two different topological approaches, namely, using Duan's topological current $\phi$-mapping theory, and the off-shell free energy. Within Duan's formalism, we observe that for a given value of the Born-Infeld parameter $b$, there exists an associated electric charge parameter $Q$, which is highly sensitive to the topological phase transitions. This way we examine the connections of the first-order phase transition and the topological nature of the critical points. We find that the topological nature has a possible breakdown in certain parametric ranges. In effect, we determine the unconventional and the conventional phase critical points as the creation (topologically vortex) and annihilation (topologically anti-vortex) points (pairs). As the second approach, we call the off-shell free energy to determine the topological classes: of which one corresponds to the AdS-Schwarzschild black hole phases, while the other provides a possible topological phase transition. Here we also reveal a novel phase transition between two unstable phases, namely, the unstable small black hole and the intermediate black holes. For a certain parametric values of the Born-Infeld parameter and the pressure, we also study the different topological descriptions that inevitably correspond to the AdS-Reissner-Nordstr$\Ddot{o}$m black hole phases. As a consistency check of the critical points during the topological phase transitions, we study the vortex/anti-vortex annihilation thermodynamics from local as well as global thermodynamic viewpoint.

hep-th↗

arXiv2023

Born-Infeld-AdS black hole phase structure: Landau theory and free energy landscape approaches

We start with a brief overview of the basic thermodynamic properties of the Born-Infeld metric in AdS spacetime. Using the concept of the enthalpy characterizing the total mass of the black hole, in our present paper, we probe the thermal phase transition structure, the dynamic and kinetic behavior of the Born-Infeld-AdS black hole. The emergence of the triple point behavior and the possible ruling out the reentrant phase transition, for a certain parametric value of the charge on the free energy landscape, we scrutinize the stochastic dynamics and the kinetic processes. We describe such processes during the black hole phase transitions in terms of the Landau functional and equivalently by the Fokker-Planck equation in the context of black hole chemistry. Our analysis establishes a pertinent bridge between the thermal behavior among the different states of the Van-der-Waals-like fluids and the Born-Infeld-AdS black holes phases. To visualize the direct implications of the Landau functional of the usual Van-der-Waals-like fluids, we consistently employed the generic Landau formalism for the analysis of the black hole phase transitions of the Born-Infeld-AdS black holes. We find that such investigations are worthy of study in implementing the continuous phase transition behavior during the Hawking radiation. For more details, and in addition to the exploitation of the Landau functional, we introduce ...

hep-th↗

arXiv2023

Revisiting the Second Law and Weak Cosmic Censorship Conjecture in High-Dimensional Charged-AdS Black Hole: an Additional Assumption

The verification of the second law of black hole mechanics and the WCCC in the context of enthalpy as mass of the black hole and its related thermodynamic properties has not been tested through a vast number of literature in the recent past. Such studies are of great physical importance as they provide us with a large number of information regarding the thermodynamics and the dynamics of AdS black hole systems. We invest the prior limited surveys of such analysis to investigate the WCCC for the $D$- dimensional asymptotically AdS-charged black holes characterized by its mass ($M$), electric charge ($Q$), and AdS radius ($l$) under the absorption of scalar particles of charge $q$. We examine the WCCC by analyzing the energy-momentum condition of the electrically charged particles as absorbed by the black holes. We prove that the conjecture is well verified irrespective of whether the initial black hole configurations are extremal or non-extremal by changing its charge, the AdS radius, and their variations. We show that the first law and the WCCC are valid for all spacetime dimensions ($D$) independent of the choice of the parameters characterizing the black holes. But to verify the second law in the extremal and non-extremal configurations one has to be very cautious as it gets strongly affected by the choices of the values of the black hole parameters and their variations... In the context of the extended phase space, taking the grand canonical potential into account allow us to obtain the missing information about the variation of the cosmological constant necessary to construct the extended phase space, namely the notion of the black hole pressure, and which is absent in the previous literature so far.

hep-th↗