Dark matter bound states via emission of scalar mediators

TL;DR

This paper investigates how scalar mediators influence the formation of dark matter bound states through emission processes, expanding understanding beyond vector mediators by including scalar potential couplings.

Contribution

It calculates the impact of scalar potential couplings on radiative capture, revealing their significance in dark matter bound state formation.

Findings

Scalar couplings can enhance bound state formation.

Parameter space where scalar effects are important is identified.

Scalar potential couplings contribute significantly to radiative transitions.

Abstract

If dark matter (DM) couples to a force carrier that is much lighter than itself, then it may form bound states in the early universe and inside haloes. While bound-state formation via vector emission is known to be efficient and have a variety of phenomenological implications, the capture via scalar emission typically requires larger couplings and is relevant to more limited parameter space, due to cancellations in the radiative amplitude. However, this result takes into account only the trilinear DM-DM-mediator coupling. Theories with scalar mediators include also a scalar potential, whose couplings may participate in the radiative transitions. We compute the contributions of these couplings to the radiative capture, and determine the parameter space in which they are important.