Static spacetimes haunted by a phantom scalar field II: dilatonic charged solutions

TL;DR

This paper develops a method to generate static solutions in Einstein-Maxwell systems with a phantom dilaton field, revealing new charged solutions and analyzing their global structures, including singularities and wormhole configurations.

Contribution

It introduces a novel formalism for constructing charged solutions with phantom dilaton fields and explores their physical properties and global spacetime structures.

Findings

Identified critical coupling constant value for phantom dilaton fields.

Derived explicit charged solutions from neutral ones, including Fisher, Gibbons, and Ellis-Bronnikov solutions.

Discovered some solutions have naked singularities, while others can form regular wormholes.

Abstract

We present a method to generate static solutions in the Einstein-Maxwell system with a (phantom) dilaton field in $n(\ge 4)$-dimensions, based upon the symmetry of the target space for the nonlinear sigma model. Unlike the conventional Einstein-Maxwell-dilaton system, there appears a critical value of the coupling constant for a phantom dilaton field. In the noncritical case, the target space is $\mathbb R\times {\rm SL}(2,\mathbb R)/H$ with the maximal subgroup $H=\{{\rm SO}(2), {\rm SO}(1,1)\}$, whereas in the critical case the target space becomes a symmetric pp-wave and the corresponding Killing vectors form a non-semisimple algebra. In either case, we apply the formalism to charge up the neutral solutions and show the analytical expression for dilatonic charged versions of (i) the Fisher solution, (ii) the Gibbons solution, and (iii) the Ellis-Bronnikov solution. We discuss global structures of these solutions in detail. It turns out that some solutions contained in the Fisher and Gibbons classes possess the parallelly propagated (p.p) curvature singularities in the parameter region where all the scalar curvature invariants remain bounded. These p.p curvature singularities are not veiled by a horizon, thrusting them into physically untenable nakedly singular spacetimes. We also demonstrate that the dilatonic-charged Ellis-Bronnikov solution admits a parameter range under which the solution represents a regular wormhole spacetime in the two-sided asymptotically flat regions.