Dilatonic dyon black hole solutions

Abstract

Dilatonic black hole dyon solutions with arbitrary dilatonic coupling constant $λ\neq 0$ and canonical sign $\varepsilon = +1$ for scalar field kynetic term are considered. These solutions are defined up to solutions of two master equations for moduli funtions. For $λ^2 \neq 1/2$ the solutions are extended to $\varepsilon = \pm 1$, where $\varepsilon = -1$ corresponds to ghost (phantom) scalar field. Some physical parameters of the solutions: gravitational mass, scalar charge, Hawking temperature, black hole area entropy and parametrized post-Newtonian (PPN) parameters $β$ and $γ$ are obtained. It is shown that PPN parameters do not depend on scalar field coupling $λ$ and $\varepsilon$. Two group of bounds on gravitational mass and scalar charge (for fixed and arbitrary extremality parameter $μ>0$) are found by using a certain conjecture on parameters of solutions when $1 +2 λ^2 \varepsilon > 0$. These bounds are verified numerically for certain examples. By product we are led to well-known lower bound on mass which was obtained earlier by Gibbons, Kastor, London, Townsend and Traschen by using spinor techniques.

20 pages, 2 figures, 2 tables, Latex. Revised version: 6 refs., 3 remarks, a paragraph in Conclusion and several sentences or phrases are added; in Sect. 5 numerics are replaced to the end