Dark Matter's secret liaisons: phenomenology of a dark U(1) sector with bound states

TL;DR

This paper analyzes a dark U(1) sector with bound states, revealing how bound-state effects influence dark matter phenomenology and constraints from cosmic-ray and CMB observations, especially for different dark photon mass ranges.

Contribution

It introduces the first comprehensive analysis of bound-state effects in dark matter models with a dark U(1) gauge symmetry, impacting detection signals and parameter constraints.

Findings

Dark matter with 1 GeV to 100 TeV mass range is largely incompatible with observations when annihilating into light dark photons.

Annihilation into heavier dark photons remains viable and consistent with experimental data.

Late decays of multi-GeV dark photons can dilute dark matter density, relaxing coupling constraints.

Abstract

Dark matter (DM) charged under a dark U(1) force appears in many extensions of the Standard Model, and has been invoked to explain anomalies in cosmic-ray data, as well as a self-interacting DM candidate. In this paper, we perform a comprehensive phenomenological analysis of such a model, assuming that the DM abundance arises from the thermal freeze-out of the dark interactions. We include, for the first time, bound-state effects both in the DM production and in the indirect detection signals, and quantify their importance for Fermi, AMS, and CMB experiments. We find that DM in the mass range 1 GeV to 100 TeV, annihilating into dark photons of MeV to GeV mass, is in conflict with observations. Instead, DM annihilation into heavier dark photons is viable. We point out that the late decays of multi-GeV dark photons can produce significant entropy and thus dilute the DM density. This can lower considerably the dark coupling needed to obtain the DM abundance, and in turn relax the existing constraints.