# Prospects for indirect dark matter searches with MeV photons

## TL;DR

This paper evaluates the potential for future MeV gamma-ray missions to detect dark matter annihilation signals in the 1 MeV to 3 GeV mass range, emphasizing spectral features like bremsstrahlung and in-flight annihilation.

## Contribution

It provides a comprehensive analysis of detection prospects for sub-GeV dark matter in the MeV range, focusing on spectral signatures often neglected in previous studies.

## Key findings

- Bremsstrahlung and in-flight annihilation are key spectral features for detection.
- Future MeV missions could significantly improve sensitivity to sub-GeV dark matter.
- Leptonic channels offer promising detection signatures.

## Abstract

Over the past decade, extensive studies have been undertaken to search for photon signals from dark matter annihilation or decay for dark matter particle masses above $\sim1$ GeV. However, due to the lacking sensitivity of current experiments at MeV-GeV energies, sometimes dubbed the 'MeV gap', dark matter models with MeV to sub-GeV particle masses have received little attention so far. Various proposed MeV missions (like, e.g., e-ASTROGAM or AMEGO) are aimed at closing this gap in the mid- or long-term future. This, and the absence of clear dark matter signals in the GeV-TeV range, makes it relevant to carefully reconsider the expected experimental instrumental sensitivities in this mass range. The most common two-body annihilation channels for sub-GeV dark matter are to neutrinos, electrons, pions or directly to photons. Among these, only the electron channel has been extensively studied, and almost exclusively in the context of the 511 keV line. In this work, we study the prospects for detecting MeV dark matter annihilation in general in future MeV missions, using e-ASTROGAM as reference, and focusing on dark matter masses in the range 1 MeV-3 GeV. In the case of leptonic annihilation, we emphasise the importance of the often overlooked bremsstrahlung and in-flight annihilation spectral features, which in many cases provide the dominant gamma-ray signal in this regime.