Gravitational analog of the canonical acoustic black hole in Einstein-scalar-Gauss-Bonnet theory

TL;DR

This paper constructs a gravitational analog of the canonical acoustic black hole within Einstein-scalar-Gauss-Bonnet theory, revealing a new class of solutions with specific horizon and photon sphere properties, and analyzing energy conditions.

Contribution

It introduces a three-parameter scalar-Gauss-Bonnet model that yields a static, spherically symmetric black hole solution with a canonical acoustic black hole structure.

Findings

The spacetime has a single horizon at r=μ^{1/4}.

A photon sphere exists at r=(3μ)^{1/4}.

For s=1, the scalar field is well-defined outside the horizon.

Abstract

In this work, in the context of modified gravity, a curved spacetime analogous to the "canonical acoustic black hole" is constructed. The source is a self-interacting scalar field which is non-minimally coupled to gravity through the Gauss-Bonnet invariant. The scalar-Gauss-Bonnet coupling function is characterized by three positive parameters: $\sigma$ with units of $(length)$, $\mu$ with units of $(length)^{4}$, and a dimensionless parameter $s$, thus defining a three-parameter model for which the line element of canonical acoustic black hole is a solution. The spacetime is equipped with spherical and static symmetry and has a single horizon determined in Schwarzschild coordinates by the region $r=\mu^{1/4}$. The solution admits a photon sphere at $r=(3\mu)^{1/4}$, and it is shown that in the region $(3\mu)^{1/4}\leq r<\infty$ the scalar field satisfies the null, weak, and strong energy conditions. Nonetheless, the model with $s=1$ has major physical relevance since for this case the scalar field is well defined in the entire region $r\geq\mu^{1/4}$, while for $s\neq1$ the scalar field blows up on the horizon.