gr-qc

Van der Waals Gravity Theory

This paper proposes a modified theory of gravity inspired by the van der Waals equation of state, which treats spacetime as a non-ideal thermodynamic system to derive field equations with a dynamical gravitational coupling that naturally resolves the initial Big Bang singularity and yields non-singular black hole solutions.

The emergence of (3+1)-dimensional expanding spacetime from complex Langevin simulations of the Lorentzian type IIB matrix model with deformations

Greybody Factor, Resonant Frequencies, and Entropy Quantization of Charged Scalar Fields in the Kerr-EMDA Black Hole

This paper investigates charged massive scalar field perturbations on the Kerr-EMDA black hole background by deriving exact analytical solutions in terms of confluent Heun functions to determine a mass-dependent resonant frequency spectrum, a parameter-dependent entropy quantization that diverges at extremality, and the first closed-form greybody factor for this geometry, thereby revealing how electromagnetic coupling and dilaton deformation fundamentally alter the black hole's wave scattering and thermodynamic properties compared to standard Kerr and Kerr-Newman cases.

Cosmology of the interacting Tsallis holographic dark energy in $f(R,T)$ gravity framework

This paper investigates the cosmological dynamics of interacting Tsallis holographic dark energy within two specific $f(R,T)$ gravity models, analyzing key parameters like the equation of state and deceleration factor to demonstrate late-time acceleration and $\Lambda$CDM consistency while constraining model parameters against observational data.

Black Hole Interiors as a Laboratory for Time-Dependent Classical Double Copy

This paper demonstrates that the trapped interiors of black holes provide an exact, time-dependent framework for the classical double copy, proving that regular solutions like the Bardeen black hole yield finite single-copy gauge fields that satisfy standard energy conditions even when the corresponding gravitational core violates them.

Two-Point Padé Approximants for the Deflection of Light in the Schwarzschild Black Hole Metric

This paper presents [2,2] two-point Padé approximants and a simpler quadratic approximation to accurately model the deflection angle of light in the Schwarzschild metric across the full range of impact parameters greater than the critical value, bridging the gap between weak-field and strong-field regimes.

Purely Quadratic Non-Gaussianity from Tachyonic Instability: Primordial Black Holes and Scalar-Induced Gravitational Waves

This paper investigates primordial black hole formation driven by purely quadratic non-Gaussianity from tachyonic instability, demonstrating that the correlation between curvature perturbations and their gradients critically determines PBH abundance and that narrow spectral widths are essential to avoid overproduction while maintaining detectable scalar-induced gravitational waves.

Regular Black Holes in General Relativity from Nonlinear Electrodynamics with de Sitter Cores

This paper presents new regular black hole solutions in general relativity supported by nonlinear electrodynamics with de Sitter cores, reconstructing their Lagrangian, analyzing their physical properties and energy conditions, constraining parameters via Event Horizon Telescope observations of Sgr A*, and verifying their dynamical stability through quasinormal mode analysis.

Thermodynamics and phase transitions of nonlinearly scalarized black holes in Einstein-scalar-Gauss-Bonnet theory

This paper investigates the thermodynamic properties of static nonlinearly scalarized black holes in Einstein-scalar-Gauss-Bonnet theory with polynomial coupling functions, demonstrating that the phase transition from Schwarzschild to scalarized black holes is first-order with non-zero latent heat.

Entropy bound and the non-universality of entanglement islands

This paper demonstrates that the entanglement island resolution to the AMPS firewall paradox cannot be universal, as the requirement for a single compact island to support all radiation regions inevitably violates the Bekenstein-Hawking entropy bound, thereby necessitating that interior reconstruction remains intrinsically region-dependent.