Signals of a Light Dark Force in the Galactic Center

TL;DR

This paper explores light dark matter models involving dark photon or scalar mediators that could explain the gamma-ray excess at the Galactic Center, fitting observational data while satisfying experimental constraints.

Contribution

It demonstrates that models with light dark mediators can produce gamma-ray spectra consistent with observations and constraints, offering a viable explanation for the Galactic Center excess.

Findings

Gamma-ray spectrum fits the Galactic Center excess.

Models predict no antiproton signals, consistent with observations.

Regions of parameter space compatible with AMS-02 constraints.

Abstract

Recent evidence for an excess of gamma rays in the GeV energy range about the Galactic Center have refocused attention on models of dark matter in the low mass regime ($m_\chi \lesssim m_Z/2$). Because this is an experimentally well-trod energy range, it can be a challenge to develop simple models that explain this excess, consistent with other experimental constraints. We reconsider models where the dark matter couples to dark photon, which has a weak kinetic mixing to the Standard Model photon, or scalars with a weak mixing with the Higgs boson. We focus on the light ($\lesssim 1.5 GeV$) dark mediator mass regime. Annihilations into the dark mediators can produce observable gamma rays through decays to $\pi^0$, through radiative processes when decaying to charged particles ($e^+e^-, \mu^+\mu^-,...$), and subsequent interactions of high energy $e^+e^-$ with gas and light. However, these models have no signals of $\bar p$ production, which is kinematically forbidden. We find that in these models, the shape of resulting gamma-ray spectrum can provide a good fit to the excess at Galactic Center. We discuss further constraints from AMS-02, and find regions of compatibility.