arXiv subjects

Mohammad Ali S Afshar

Publications and source records attributed to Mohammad Ali S Afshar.

3 recordsLinked to original sources

arXiv2026

Testing the Weak Gravity Conjecture via Gravitational Lensing, Black Hole Shadows, and Barrow Thermodynamics in F(R)-Euler-Heisenberg (A)dS Black Holes

We investigate the interplay of the Weak Gravity Conjecture (WGC) and the Weak Cosmic Censorship Conjecture (WCCC) in $F(R)$-Euler-Heisenberg black holes in Anti-de Sitter and de Sitter backgrounds. The solution is characterized by the electric charge $q$, the $F(R)$ deviation $f_{R_0}$, the Euler--Heisenberg coupling $λ$, and the constant scalar curvature $R_0$. We establish a universal entropy--extremality relation that provides thermodynamic evidence for the WGC independently of $f_{R_0}$ and $R_0$. Photon sphere analysis from both geodesic and topological perspectives confirms the simultaneous compatibility of the WGC and WCCC, with the Euler--Heisenberg coupling restoring photon spheres in the naked singularity regime. Gravitational lensing in the strong- and weak-deflection limits reveals that the photon sphere radius is independent of the cosmological background while the critical impact parameter nearly doubles in de Sitter. Black hole shadow images under isotropic accretion are constructed. Within the Barrow entropy framework, we uncover van der Waals-type phase transitions and analyze Joule-Thomson expansion, identifying the small black hole phase as the WGC-compatible thermodynamic regime accessible via isenthalpic cooling.

gr-qc↗

arXiv2025

Swampland Conjectures through ACT Observations: Observational Signatures of Radiative-Corrected Inflation

We investigate the consistency of radiatively corrected inflationary models with both the latest observational data from the Atacama Cosmology Telescope (ACT) combined with Planck 2018 and Baryon Acoustic Oscillation (BAO) measurements, and the theoretical constraints imposed by the swampland program. We systematically test two distinct models against three key swampland conjectures: the further refined de Sitter swampland conjecture (FRDSSC), the scalar weak gravity conjecture (SWGC), and the strong scalar weak gravity conjecture (SSWGC). Model I, based on radiatively corrected Higgs inflation, satisfies the FRDSSC and remains consistent with current observational constraints ($n_s = 0.9743 \pm 0.0034$, $r < 0.038$), but fails to meet the SWGC and SSWGC requirements, indicating limited theoretical compatibility with quantum gravity principles. In contrast, Model II, incorporating radiative corrections with scalar sectors, demonstrates full consistency by satisfying all three swampland conjectures simultaneously while maintaining observational viability. The compatibility of Model II is highly sensitive to the non-minimal coupling $ξ$ and renormalization scales $μ_b$, with larger values extending the range of swampland-consistent solutions. Our results highlight the critical role of radiative corrections in achieving simultaneous theoretical and observational consistency, and identify Model II as a promising candidate for a fully viable inflationary scenario within the swampland framework. This work provides a methodology for classifying inflationary models based on their swampland compatibility, demonstrating that satisfaction of the FRDSSC alone is insufficient for full theoretical consistency.

astro-ph.CO↗

arXiv2025

Probing the Weak Gravity Conjecture: Novel Aschenbach Signatures in Superextremal Non-Linear Charged AdS Black Holes

This study investigates the nonlinear charged Anti-de Sitter (AdS) black hole solution within the framework of massive gravity, motivated by recent advancements linking the Weak Gravity Conjecture (WGC) to phenomena such as Weak Cosmic Censorship Conjecture (WCCC) and photon sphere dynamics. Building on these foundations, we focus on the Aschenbach effect-a relativistic phenomenon intricately tied to the geometry of photon spheres and known to occur in some special sub-extremal non rotating black holes. Our primary objective is to determine whether this effect persists not only up to the extremal limit but also beyond, into the superextremal regime, thus probing the stability and validity of black hole characteristics in these extreme conditions. By analyzing the nonlinear charged AdS black hole solutions in massive gravity, we demonstrate that the Aschenbach effect remains a robust feature across both extremal and superextremal configurations. This extension suggests that key relativistic signatures and the underlying spacetime structures associated with high-spin black holes continue to hold beyond classical boundaries. Our results provide new insights into the behavior of ultra-compact objects and highlight promising directions for exploring the limits of general relativity, as well as potential generalizations of the WGC and WCC in strong gravitational fields.

gr-qc↗