Dyonic Einstein-Maxwell-scalar black holes: the cold, the hot and the plunge

TL;DR

This paper explores the existence and properties of dyonic scalarized black holes in Einstein-Maxwell-scalar theory, revealing three distinct branches with unique thermodynamic behaviors and a critical plunge in temperature linked to charge interactions.

Contribution

It introduces the analysis of dyonic scalarized black holes with multiple charge branches and demonstrates the conditions for extremality and temperature plunge in this context.

Findings

Three branches of scalarized dyonic black holes identified.

Existence of regular extremal black holes with both charges.

Temperature plunges at a critical scalar field value.

Abstract

We investigate dyonic nonlinearly scalarized black holes in Einstein-Maxwell-scalar theory. The domain of existence of scalarized dyonic black holes consists of three branches. The cold branch and the hot branch bifurcate at a minimal value of the charge, analogous to the purely electrically charged scalarized black holes. However, the presence of both charges allows for regular extremal black holes, leading to a third branch featuring a sudden plunge in Hawking temperature. In fact, the presence of both electromagnetic charges introduces a factor $\Delta(\phi)$ in the source term of scalar field equations that vanishes when the coupling function $f(\phi)$ equals the ratio of the charges for some value of the scalar field $\phi_c$. The scalar field of extremal black holes assumes precisely this value at the horizon, $\phi_H=\phi_c$. We demonstrate the plunge for the coupling function $f(\phi)=\exp(\alpha \phi^3)$.