# Gamma-ray line constraints on Coy Dark Matter

## TL;DR

Coy dark matter models, involving a fermionic dark matter particle and a pseudoscalar mediator, can explain the Galactic Center gamma-ray excess while evading direct detection constraints, but future gamma-ray experiments are needed for full testing.

## Contribution

This work analyzes the gamma-ray line signatures of coy dark matter, assessing its viability against current observations and highlighting the potential of upcoming experiments to probe the model.

## Key findings

- Gamma-ray line constraints exclude part of the parameter space.
- The model remains compatible with the Galactic Center excess.
- Next-generation experiments can thoroughly test the scenario.

## Abstract

Coy dark matter is an effective scheme in which a fermionic dark matter candidate interacts with the Standard Model fermions via a pseudoscalar mediator. This simple setup avoids the strong constraints posed by direct detection experiments in a natural way and explains, on top of the observed dark matter relic abundance, the spatially extended gamma-ray excess recently detected at the Galactic Center. In this Letter we study the phenomenology of coy dark matter accounting for a novel signature of the model: the diphoton annihilation signal induced by the Standard Model fermions at the loop level. By challenging the model with the observations of spheroidal dwarf satellite galaxies and the results of gamma-ray line searches obtained by the Fermi LAT experiment, we assess its compatibility with the measured dark matter relic abundance and the Galactic Center excesses. We show that despite the gamma-ray line constraint rules out a significant fraction of the considered parameter space, the region connected to the observed Galactic Center excess remains currently viable. Nevertheless, we find that next-generation experiments such as DAMPE, HERD and GAMMA-400 have the potential to probe exhaustively this elusive scenario.