Dark Grand Unification in the Axiverse: Decaying Axion Dark Matter and Spontaneous Baryogenesis

TL;DR

This paper explores heavy axion-like particles from dark gauge groups as dark matter candidates, their potential decay signatures, and their role in baryogenesis, within a GUT-unified dark sector framework.

Contribution

It introduces models with GUT-scale decay constant axions in the axiverse, explaining dark matter abundance, decay signatures, and baryogenesis mechanisms.

Findings

Heavy axions can account for dark matter via misalignment and early matter domination.

Decaying axions produce detectable photon signatures for future telescopes.

Dark gauge groups can unify with the Standard Model at GUT scale, enabling spontaneous baryogenesis.

Abstract

The quantum chromodynamics axion with a decay constant near the Grand Unification (GUT) scale has an ultralight mass near a neV. We show, however, that axion-like particles with masses near the keV - PeV range with GUT-scale decay constants are also well motivated in that they naturally arise from axiverse theories with dark non-abelian gauge groups. We demonstrate that the correct dark matter abundance may be achieved by the heavy axions in these models through the misalignment mechanism in combination with a period of early matter domination from the long-lived dark glueballs of the same gauge group. Heavy axion dark matter may decay to two photons, yielding mono-energetic electromagnetic signatures that may be detectable by current or next-generation space-based telescopes. We project the sensitivity of next-generation telescopes including $\textit {Athena,}$ AMEGO, and e-ASTROGAM to such decaying axion dark matter. If the dark sector contains multiple confining gauge groups, then the observed primordial baryon asymmetry may also be achieved in this scenario through spontaneous baryogenesis. We present explicit orbifold constructions where the dark gauge groups unify with the SM at the GUT scale and axions emerge as the fifth components of dark gauge fields with bulk Chern-Simons terms.