Dyonic black holes and dilaton charge in string theory

Abstract

We present the four-dimensional non-extremal dyonic black hole solution for Einstein-Maxwell-dilaton theory in absence of a scalar potential written in terms of integration constants only. These integration constants must satisfy a set of conditions imposed by the equations of motion. By defining a posteriori the mass $M$ of the black hole and the dilaton charge $\Sigma$, we show how to recover the dyonic black hole solution found by Kallosh et.al. In particular, our analysis show that there is a possibility in defining whether the dilaton charge or the mass of the black hole is an independent parameter. When the mass of the black hole is the independent parameter, then there is a well-defined limit in which the dilaton charge is zero. For this case, it is straightforward to provide an answer to why is $\phi_{H, \text{extreme}}$ independent of $\phi_{0}$ and to why $\phi_{H, \text{extreme}}=\phi_{0}$ when the dilaton charge is zero.