International Journal of Modern Physics A

In this invited review, we discuss the evaporation of a black hole, with emphasis on the resulting macroscopically distinct patterns of Hawking radiation. The density matrix of this radiation can approach a pure final state in the form of a highly entangled macroscopic superposition state. We note that this exact property is exhibited in replica wormhole calculations, and also in quantum hair effects on Hawking radiation amplitudes. Finally, we revisit the information paradox (Mathur’s theorem and firewalls), showing that it can be resolved by macroscopic entanglement.

In this work, we investigated the influence on the evolution of gas of thin tubes of a massless scalar field, in particular, on its ability to accelerated expansion, of such characteristics of thin tubes forming gas as thickness (core radius), the moment of their formation and spatial shape. The study showed that the formation of thin tubes of a scalar field that form gas becomes possible only some time after the singular state of the Universe. At the same time, the thinner the tubes form a gas, and the later in the process of evolution they were formed, the faster such a gas can achieve the equation of state $p=-\rho$.

In this paper, we study the solutions of Einstein’s field equations in Einstein–Maxwell-dilaton gravity. By presenting the (3+1)-dimensional action in which gravity is coupled to a dilaton field, we derive the field equations. We present a new class of charged dilaton black hole solutions in Einstein–Maxwell-dilaton theory and investigate the effects of dilaton field on the properties of space–time. We show that these solutions are physical and describe spherically symmetric charged black holes. The calculated potential is Liouville type and has two rules. The exact solution of the field equations leads to the production of the metric function with three rules. By examining the physical properties of the solutions, we find the mass, charge, electric potential and temperature of charged dilaton black holes. Also, with the help of the canonical ensemble method, we study the thermodynamics and thermal stability of solutions and show the effects of dilaton and Maxwell fields on the thermodynamics of these solutions. Finally, by examining the phase transition of the solutions, we present thermal stability of the black hole in (3+1)-dimensional.

The study reports on the attainment of bound state solutions and the associated relativistic energy eigenvalues of the Dirac equation in the presence of a modified double ring shaped generalized Cornell potential. This is accomplished by using the extended Nikiforov–Uvarov method, which prioritizes the elimination of complexities in determining ansatzs or employing series expansions. In particular, the wave functions are expressed in terms of Heun type polynomials.

In this paper, we obtain $L^{\infty }$ estimate for the Maxwell–Higgs system in the exterior region of Reissner–Nordström spacetimes. Utilizing the integrated local energy decay estimate, the Sobolev embedding theorem alongside the Gagliardo–Nirenberg–Sobolev inequality on compact Riemannian manifold, we derive the boundedness for $L^{\infty }$ norm of the Maxwell–Higgs system on Reissner–Nordström geometry.

A new interior solution of Einstein’s equations is derived for a static and spherically symmetric space–time that contains fluid with anisotropic pressures, characterized by a parameter N. The model presented is a generalization to a proposal which contemplated a perfect fluid, which allows us to do an analysis of the impact of the anisotropy on the compactness, density and speed of sound. Taking the observational data of the mass $M=1.7M_{\odot }$ and radius $R=9$ km as well as the mass $M=1.4M_{\odot }$ and radius $R=11$km reported for the star EXO 1745-248, it is determined that the range of values of the density varies between $5.7651\times 10^{17}$ and $1.0937\times 10^{18}$ and these increase as the anisotropy parameter increases; it also shows an effect of the anisotropy on the speed of sound. The stability of the solution is shown through the Zeldovich criteria and through the adiabatic index, and from a graphic analysis it is verified that the behavior of the density, pressures and speed of sound are physically acceptable.

The influence of noncommutativity on the local stability of the accelerating (un)charged Schwarzschild black hole is what we aim to investigate. It results in the C-metric description of accelerating Schwarzschild black hole. Such a notion describes a pair of separated black holes that accelerate in opposite directions under the action of forces represented by conical singularities. However, the impact of spatial noncommutativity on the thermodynamic properties of an accelerating (un)charged Schwarzschild black hole is explored by analyzing the Gaussian distribution of mass and charge densities, reflecting the smearing effects due to noncommutative geometry. We begin the study with the uncharged case, examining the influence of noncommutativity and acceleration. This approach highlights how these parameters jointly modify the temperature, entropy, and heat capacity of the black hole, deviating from classical thermodynamics. Next, the charged case is considered, introducing additional complexity as charge density now interacts with both noncommutativity and acceleration. This scenario reveals further modifications in the black hole’s thermodynamic behavior. The effects of noncommutativity and acceleration are reexamined, revealing further interactions and modifications of the black hole’s thermodynamic properties. By addressing these two cases sequentially, the paper offers new insights into black holes in noncommutative and accelerated geometries.

We study thermodynamics and thermal stability of three-dimensional (3D) charged black holes (BHs) in the Brans–Dicke (BD) gravity theory. The BD field equations, which are written in the Jordan frame, are nonlinear and too complex for direct solving. Thus, by utilizing the conformal transformations (CT), we translated them to the Einstein frame, where the equations are solved easier. In the Einstein–Maxwell-dilaton (EMd) theory, the number of unknowns is one more than the unique equations. Thus, we solved this problem by using an exponential ansatz function and introduced four novel classes of 3D EMd BHs with unusual asymptotic behavior. We proved validity of the first law of BH thermodynamics (FLT), and explored thermal stability of the EMd BHs by use of the canonical ensemble method. We introduced 3D BD-Maxwell BHs by applying the inverse CT on the Einstein frame counterparts. By using the plots, we showed that our solutions can produce BD BHs without horizon, with one or two horizons. By direct calculations, we proved that thermodynamic quantities are conformal-invariant and FLT is valid for the BD BHs too. Moreover, stability properties of the BD BHs are just like those of EMd ones.