On horizons and wormholes in k-essence theories

TL;DR

This paper investigates static, spherically symmetric solutions in k-essence theories, proving a no-go theorem for finite-radius horizons under certain conditions and presenting exact solutions illustrating horizons and wormholes.

Contribution

It establishes a no-go theorem for black-hole-like horizons in k-essence with finite derivative functions and provides explicit solutions demonstrating horizons and wormholes.

Findings

No finite-radius horizon exists if dF/dX is finite.

Two exact solutions with horizons are found, one describing a black hole in a singular space-time.

A wormhole connecting two horizons of infinite area is constructed.

Abstract

We study the properties of possible static, spherically symmetric configurations in k-essence theories with the Lagrangian functions of the form $F(X)$, $X \equiv \phi_{,\alpha} \phi^{,\alpha}$. A no-go theorem has been proved, claiming that a possible black-hole-like Killing horizon of finite radius cannot exist if the function $F(X)$ is required to have a finite derivative $dF/dX$. Two exact solutions are obtained for special cases of k-essence: one for $F(X) =F_0 X^{1/3}$, another for $F(X) = F_0 |X|^{1/2} - 2 \Lambda$, where $F_0$ and $\Lambda$ are constants. Both solutions contain horizons, are not asymptotically flat, and provide illustrations for the obtained no-go theorem. The first solution may be interpreted as describing a black hole in an asymptotically singular space-time, while in the second solution two horizons of infinite area are connected by a wormhole.