Galactic Center Gamma-Ray Excess through a Dark Shower

TL;DR

This paper proposes a novel dark matter model involving a hidden valley sector that explains the galactic center gamma-ray excess without conflicting with existing experimental constraints.

Contribution

It introduces a strongly coupled hidden sector where dark matter annihilates into hidden quarks, which then decay into photons, providing a new viable explanation for the gamma-ray excess.

Findings

Fits the gamma-ray spectrum with ~10 GeV dark matter and ~1 GeV confinement scale.

Prefers an SU(2) hidden confining gauge group over SU(3).

Discusses phenomenology and experimental constraints of the model.

Abstract

The reported excess of $\gamma$-rays, emitted from an extended region around the galactic center, has a distribution and rate suggestive of an origin in dark matter (DM) annihilations. The conventional annihilation channels into standard model (SM) $b$ quarks or $\tau$ leptons may, however, be in tension with various experimental constraints on antiproton and positron fluxes. We present a framework that is free from such constraints. The key idea is that the mediators between the dark matter and the SM are themselves part of a strongly coupled sector: a hidden valley. In this scenario, the dark matter particles annihilate only into hidden quarks that subsequently shower and hadronize. Hidden quark effective couplings to SM hypercharge allow the lightest hidden bound states to subsequently decay into SM photons, producing the observed photon energy spectrum. Associated production of SM fermions is, in contrast, suppressed by electroweak, loop or helicity effects. We find that, generically, $\sim$ 10 GeV DM and a confinement scale $\sim$ 1 GeV provide a good fit to the observed spectrum. An $SU(2)$ hidden confining group is preferred over $SU(3)$ or higher rank gauge groups, up to uncertainties in the extraction of the astrophysical background. An explicit realization of this framework is also presented, and its phenomenology is discussed in detail, along with pertinent cosmological, astrophysical and collider bounds. This framework may be probed by model-independent searches, including future beam-dump experiments.