# Gamma Ray Spectra from Dark Matter Annihilation and Decay

## TL;DR

This paper analyzes gamma ray spectra from dark matter annihilation and decay, focusing on scenarios compatible with PAMELA data, comparing direct photon production, final state radiation, and higher-order operator contributions.

## Contribution

It provides a detailed comparison of gamma ray spectra from various dark matter processes, highlighting the dominance of higher-order operators at certain energy scales.

## Key findings

- Higher-order operators dominate photon spectra for dark matter masses around 1 TeV if their scale is below 1000 TeV.
- Final state radiation produces softer gamma ray spectra compared to higher-order operators.
- The hardest gamma ray spectra arise from higher-order operators, while the softest come from intermediate decay final state radiation.

## Abstract

In this paper, we study gamma ray spectra for various scenarios of dark matter annihilation and decay. We focus on processes which generate only high-energy photons or leptons and photons, but no proton-antiproton pairs, to be compatible with PAMELA's data. We investigate photons produced directly from two-body decay chains and photons produced together with charged particles. For the former case we also include the process DM(+DM) -> N phi -> 2N gamma which can arise from specific strongly-coupled dark matter scenarios. For the latter case, photons are either generated by final state radiation from high-energy leptons or are directly generated from contact interactions represented by higher-order (non-renormalizable) operators obtained after integrating out heavy modes. We compare their overall annihilation cross-sections/decay rates taking into account chiral suppression (in the s-wave approximation), dimension of operators and dark matter particle properties. A rough estimate shows that, for a dark matter particle with a mass of O(1 TeV), the hard photon spectra in direct electron-positron-photon final states arising from either scalar boson dark matter annihilation/decay or Majorana fermion dark matter annihilation are dominated by higher-order operators if the scale of the leading operator is lower than O(1000 TeV). Otherwise, all the photon spectra arising in this way are dominated by final state radiation. Among the spectra studied, the higher-order operators spectrum is the hardest while the final state radiation spectrum with an intermediate decay is the softest.