Dilatonic (quasi-) black holes without scalar charge

Abstract

We consider static, spherically symmetric configurations of electrically charged dust in Einstein-Maxwell-dilaton gravity where the Lagrangian contains the interaction term P(χ)F_μνF^μν with an arbitrary function P(χ). Unlike previous studies, we assume that the scalar field χ (which can be canonical or phantom) does not have a charge of its own and exists only due to this interaction. We discuss possible solutions to the field equations, in particular, those describing black holes (BHs) and quasi-black holes (QBHs). The latter are globally regular configurations whose size is very close to that of a BH of the same mass and which therefore are almost indistinguishable from BHs for a distant observer. Some general features are revealed, a family of explicitly integrable models is found, and some explicit examples are presented.