Charged AdS black holes with finite electrodynamics in 4D Einstein-Gauss-Bonnet gravity

Using a modified expression for the electric potential in the context of T-duality [Gaete and Nicolini, Phys. Lett. B, 2022], we obtained an exact charged solution within the 4D Einstein-Gauss-Bonnet (4D EGB) theory of gravity in the presence of a cosmological constant. We show that the solution also exists in the regularized 4D EGB theory. Moreover, we point out a correspondence between the black hole solution in the 4D EGB theory and the solution in the non-relativistic Horava–Lifshitz theory. The black hole solution is regular and free from singularity. As a special case, we derive a class of well known solutions in the literature.

Quantum effects on the black hole shadow and deflection angle in the presence of plasma

In this study,the optical properties of a renormalization group improved(RGI)Schwarzschild black hole(BH)are investigated in a plasma medium.Beginning with the equations of motion in a plasma medium,we aim to present the modifications in the shadow radius of the RGI BH.To this end,we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media.Importantly,owing to the plasma media,we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified.This,in turn,changes and modifies the expression for the intensity observed far away from the BH.Finally,we obtain the shadow images for the RGI BH for different plasma models.Although quantum effects change the background geometry,such effects are minimal,and practically detecting these effects using the current technology based on supermassive BH shadows is impossible.The parameterΩencodes the quantum effects,and in principle,one expects such quantum effects to play significant roles only for very small BHs.However,the effects of plasma media can play an important role in the optical appearance of BHs,as they affect and modify the equations of motion.

Stable gravastars： Guilfoyle＇s electrically charged solutions

Compelling alternatives to black holes, namely, gravitational vacuum stars （gravastars）, which are multilayered compact objects, have been proposed to avoid a number of theoretical problems associated with event horizons and singularities. In this work, we construct a spherically symmetric thin-shell charged gravastar model where the vacuum phase transition between the de Sitter interior and the external Reissner-Nordstrom spacetime （RN） are matched at a junction surface, by using the cut-and-paste procedure. Gravastar solutions are found among the Guilfoyle exact solutions where the gravitational potential We and the electric potential field Ф obey a particular relation in a simple form a（b-εФ）^2＋b1, where a, b and bl are arbitrary constants. The simplest ansatz of Guilfoyle＇s solution is implemented by the following assumption： that the total energy density 8πρm＋Q^2/r^4 is constant, where Q（r） is the electric charge up to a certain radius r. We show that, for certain ranges of the parameters, we can avoid the horizon formation, which allows us to study the linearized spherically symmetric radial perturbations around static equilibrium solutions. To lend our solution theoretical support, we also analyze the physical and geometrical properties of gravastar configurations.