Galactic Center Excess in Gamma Rays from Annihilation of Self-Interacting Dark Matter

TL;DR

This paper proposes a self-interacting dark matter model with a 50 GeV particle and a light mediator to explain the gamma-ray excess at the Galactic Center while remaining consistent with dwarf galaxy observations and other constraints.

Contribution

It introduces a novel self-interacting dark matter model with a light mediator that simultaneously explains gamma-ray excess and galaxy density observations.

Findings

The model fits the gamma-ray excess data.

It predicts detectable signatures unique to self-interacting dark matter.

The mediator mass must be below 100 MeV to affect dwarf galaxy densities.

Abstract

Observations by the Fermi-LAT telescope have uncovered a significant $\gamma$-ray excess toward the Milky Way Galactic Center. There has been no detection of a similar signal in the direction of the Milky Way dwarf spheroidal galaxies. Additionally, astronomical observations indicate that dwarf galaxies and other faint galaxies are less dense than predicted by the simplest cold dark matter models. We show that a self-interacting dark matter model with a particle mass of roughly 50 GeV annihilating to the mediator responsible for the strong self-interaction can simultaneously explain all three observations. The mediator is necessarily unstable and its mass must be below about 100 MeV in order to lower densities in faint galaxies. If the mediator decays to electron-positron pairs with a cross section on the order of the thermal relic value, then we find that these pairs can up-scatter the interstellar radiation field and produce the observed $\gamma$-ray excess. We show that this model is compatible with all current constraints and highlight detectable signatures unique to self-interacting dark matter models.