Black Holes in Magnetic Monopoles with a Dark Halo

TL;DR

This paper explores how scalar fields coupled to magnetic monopoles and black holes can form halos or lead to different solution regimes, revealing complex phase structures influenced by scalar interactions.

Contribution

It introduces a phase diagram for self-gravitating monopole solutions with a scalar halo, highlighting the effects of Higgs portal coupling and scalar potential parameters.

Findings

Halo formation depends on Higgs portal coupling strength

Large coupling leads to black hole-monopole solutions without halos

Bound on Higgs potential coupling for solution stability

Abstract

We study a spontaneously broken Einstein-Yang-Mills-Higgs model coupled via a Higgs portal to an uncharged scalar $\chi$. We present a phase diagram of self-gravitating solutions showing that, depending on the choice of parameters of the $\chi$ scalar potential and the Higgs portal coupling constant $ \gamma$, one can identify different regions: If $\gamma$ is sufficiently small a $\chi$ halo is created around the monopole core which in turn surrounds a black-hole. For larger values of $\gamma$ no halo exists and the solution is just a black hole-monopole one. When the horizon radius grows and becomes larger than the monopole radius solely a black hole solution exists. Because of the presence of the $\chi$ scalar a bound for the Higgs potential coupling constant exists and when it is not satisfied, the vacuum is unstable and no non-trivial solution exists. We briefly comment on a possible connection of our results with those found in recent dark matter axion models.