Charged black holes in string-inspired gravity II. Mass inflation and dependence on parameters and potentials

Abstract

We investigate the relation between the existence of mass inflation and modelparameters of string-inspired gravity models. In order to cover various models, we investigatea Brans-Dicke theory that is coupled to a U(1) gauge field. By tuning a model parameterthat decides the coupling between the Brans-Dicke field and the electromagnetic field, wecan make both of models such that the Brans-Dicke field is biased toward strong or weakcoupling directions after gravitational collapses. We observe that as long as the Brans-Dickefield is biased toward any (strong or weak) directions, there is no Cauchy horizon and no massinflation. Therefore, we conclude that to induce a Cauchy horizon and mass inflation insidea charged black hole, either there is no bias of the Brans-Dicke field as well as no Brans-Dicke hair outside the horizon or such a biased Brans-Dicke field should be well trapped andcontrolled by a potential.