Hidden On-Shell Mediators for the Galactic Center Gamma-Ray Excess

Abstract

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.

Comments: 21 pages + appendix + references, 11 figures, 3 tables. v2: minor revisions, additional figure and table for clarity, references added. v3: copyedit corrections, update references