Lining up the Galactic Center Gamma-Ray Excess

Abstract

Dark matter particles annihilating into Standard Model fermions may be able to explain the recent observation of a gamma-ray excess in the direction of the Galactic Center. Recently, a hidden photon model has been proposed to explain this signal. Supplementing this model with a dipole moment operator and a small dark sector mass splitting allows a large cross section to a photon line while avoiding direct detection and other constraints. Comparing the line and continuum cross sections, we find that the line is suppressed only by the relative scales and couplings. Given current constraints on this ratio, a line discovery in the near future could point to a new scale Lambda ~ O(1 TeV), where we would expect to discover new charged particles. Moreover, such a line would also imply that dark matter can be visible in near-future direct detection experiments.