Bardeen Black Holes in the Regularized $4D$ Einstein--Gauss--Bonnet Gravity

Abstract

We obtain exact Bardeen black holes to the regularized $4D$ Einstein--Gauss--Bonnet (EGB) gravity minimally coupled with the nonlinear electrodynamics (NED). In turn, we analyze the horizon structure to determine the effect of GB parameter $\hat{I}\pm$ on the minimum cutoff values of mass, $M_0$, and magnetic monopole charge, $g_0$, for the existence of a black hole horizon. We obtain an exact expression for thermodynamic quantities, namely, Hawking temperature $T_{+}$, entropy $S_{+}$, Helmholtz free energy $F_{+}$, and specific heat $C_{+}$ associated with the black hole horizon, and they show significant deviations from the $4D$ EGB case owing to NED. Interestingly, there exists a critical value of horizon radius, $r_{+}^c$, corresponding to the local maximum of Hawking temperature, at which heat capacity diverges, confirming the second-order phase transition. A discussion on the black holes of alternate regularized $4D$ EGB gravity belonging to the scalar-tensor theory is appended.

15 pages and 4 figures. This was an invited manuscript published in the special issue "Dark Matter and Dark Energy: Particle Physics, Cosmology, and Experimental Searches"