Dark Forces in the Sky: Signals from Z' and the Dark Higgs

TL;DR

This paper explores a hidden U(1) dark matter model with a dark Higgs and Z' boson, revealing a new dominant annihilation channel that enhances indirect detection prospects and constrains model parameters using astrophysical data.

Contribution

It introduces a two-mediator dark sector model with a novel s-wave annihilation channel, expanding the phenomenological analysis beyond simplified models.

Findings

The new $ ext{χ}ar{ ext{χ}} ightarrow sZ'$ channel can dominate dark matter annihilation.

This channel allows probing of parameter space inaccessible to single-mediator models.

Fermi data constrains the model's parameters based on dwarf spheroidal galaxy observations.

Abstract

We consider the indirect detection signals for a self-consistent hidden $U(1)$ model containing a Majorana dark matter candidate, $\chi$, a dark gauge boson, $Z'$, and a dark Higgs, $s$. Compared with a model containing only a dark matter candidate and $Z'$ mediator, the addition of the scalar provides a mass generation mechanism for the dark sector particles and is required in order to avoid unitarity violation at high energies. We find that the inclusion of the two mediators opens up a new two-body s-wave annihilation channel, $\chi\overline\chi\rightarrow sZ'$. This new process, which is missed in the usual single-mediator simplified model approach, can be the dominant annihilation channel. This provides rich phenomenology for indirect detection searches, allows indirect searches to explore regions of parameter space not accessible with other commonly considered s-wave annihilation processes, and enables both the $Z'$ and scalar couplings to be probed. We examine the phenomenology of the sector with a focus on this new process, and determine the limits on the model parameter space from Fermi data on dwarf spheriodal galaxies and other relevant experiments.