Mohammad Ali Salahshour Afshar

In this paper, we investigate the compatibility of eternal inflation with three recently proposed swampland-inspired criteria: The Further Refined de Sitter Swampland Conjecture (FRDSSC), the Scalar Weak Gravity Conjecture (SWGC), and the Strong Scalar Weak Gravity Conjecture (SSWGC). Our analysis reveals that while the FRDSSC permits eternal inflation within a narrow hilltop regime where quantum diffusion dominates over classical rolling near a tachyonic maximum the SWGC and SSWGC impose significantly stronger constraints. In single-field hilltop models, which we analyze in this work, these scalar weak gravity conditions are generically violated, thereby disfavoring eternal inflation unless additional fields, non-hilltop potential shapes, or multi-field dynamics are introduced. These results delineate a nuanced landscape in which eternal inflation can survive under refined de Sitter conditions but remains highly constrained by scalar weak gravity considerations within the class of models studied here. Importantly, our findings do not amount to an absolute exclusion of eternal inflation in all single field cases; rather, they indicate that eternal inflation is generically disfavored under the SWGC and SSWGC, with possible viable alternatives requiring specially constructed potentials or extended frameworks. This work provides critical insights into the interplay between quantum gravity, inflationary dynamics, and the string landscape.

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–Nordström (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.

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 Rényi entropy measures. The primary objective is to examine the possibility of an intrinsic link and mutual influence between the noncommutative parameter( θ ) and the parameters arising from generalized entropies. By analyzing both Tsallis and Rényi frameworks, we investigate whether a fundamental relationship exists between θ and the entropy index q . Establishing such a connection could provide new insights into the interplay between spacetime geometry and generalized statistical mechanics.

Static spheres in spherically symmetric black hole spacetimes are special equilibrium surfaces where massive test particles can remain at rest with respect to asymptotic static observers without orbital motion. Their existence is closely related to the structure of timelike and null geodesics and has attracted attention as a distinctive feature of modified black hole geometries. Previous studies have shown that static spheres and Aschenbach-like non-monotonic angular velocity profiles in non-rotating black holes can arise in the presence of nonlinear electromagnetic or scalar field contributions. In this work, we investigate whether such geodesic structures can also emerge from an effective geometric deformation of a Schwarzschild spacetime. For this purpose, we employ a hairy Schwarzschild black hole solution generated through the extended gravitational decoupling (EGD) framework, in which the deformation of the metric is encoded by an effective source θµν without specifying a fundamental matter Lagrangian. We show that the resulting geometry can support both a non-monotonic angular velocity profile, analogous to the Aschenbach effect in static spacetimes, and static sphere configurations determined by the condition g ′ tt(rsp) = 0. Our results demonstrate that these geodesic phenomena are not exclusively associated with rotation or explicit nonlinear matter couplings, but can also arise from suitable effective modifications of spacetime geometry. This provides a broader framework for studying nontrivial orbital structures in black hole spacetimes and motivates further investigations of their possible implications, including speculative connections with Dyson-like configurations around compact objects.

In this work, we study some aspects of thermodynamic universality, topology, and geometry of charged anti-de Sitter (AdS) black holes within the framework of Hořava–Lifshitz gravity. The universal relation is established, demonstrating how the weak gravity conjecture manifests within the thermodynamic behavior of these black holes. Further, by employing vector field analysis, the distribution and stability of topological charges are examined, and some points corresponding to localized charge structures are identified, revealing that the total topological charge remains conserved despite variations in system parameters. The results are consistent with standard black hole classifications, confirming the robustness and reliability of the topological framework. Next, we compute thermodynamic curvature and phase behavior, which reveals a transition in the dominant microscopic interactions governing the black hole microstructures from repulsive to attractive type interactions. This transition occurs, indicating that modifications in gravity and charge play crucial roles in shaping interactions among the microstructures. Furthermore, the photon sphere structure is investigated and shown to exhibit topological invariance under continuous parameter variations, providing an additional means of characterizing the system.