Hidden On-Shell Mediators for the Galactic Center Gamma-Ray Excess
  We present simplified models for the galactic center gamma-ray excess where Dirac dark matter annihilates into pairs or triplets of on-shell bosonic mediators to the Standard Model. These annihilation modes allow the dark matter mass to be heavier than those of conventional effective theories for the gamma-ray excess. Because the annihilation rate is set by the dark matter--mediator coupling, the Standard Model coupling can be made parametrically small to `hide' the dark sector by suppressing direct detection and collider signals. We explore the viability of these models as a thermal relic and on the role of the mediators for controlling the gamma-ray spectral shape. We comment on ultraviolet completions for these simplified models and novel options for Standard Model final states. 
Mohammad Abdullah, Anthony DiFranzo, Arvind Rajaraman, Tim M. P. Tait,   Philip Tanedo, Alexander M. Wijangco
hep-ph astro-ph.HE