Non-Abelian monopoles in Einstein-scalar-Gauss-Bonnet gravity

Abstract

We study static, spherically symmetric self-gravitating non-Abelian 't Hooft-Polyakov monopoles in Einstein-scalar-Gauss-Bonnet gravity for two classes of scalar-Gauss-Bonnet coupling functions. We demonstrate that the branch structure of the monopole solutions depends sensitively on the choice of the coupling function. For the polynomial coupling, we show that, for sufficiently large values of the coupling parameter, the principal part of the field equations becomes locally degenerate at a critical radius, leading to a critical solution that signals a geometric phase transition. By contrast, the exponential coupling acts as a natural regulator, preventing the degeneration of the principal part and preserving smooth field profiles. Finally, we discuss a possible physical interpretation of the critical solution, in which spacetime separates into an inner region where quantum-gravitational effects may become important and an outer region that remains well described by classical general relativity.