Hunting Dark Matter Gamma-Ray Lines with the Fermi LAT

TL;DR

This paper reports a comprehensive search for gamma-ray lines in Fermi LAT data as potential signatures of dark matter, setting constraints on dark matter models and discussing implications for supersymmetric scenarios.

Contribution

It provides the first detailed analysis of gamma-ray line signals in the 1-300 GeV range using two years of Fermi LAT data, with implications for dark matter models.

Findings

No significant gamma-ray line detected at 5-sigma level.

Established conservative bounds on dark matter decay and annihilation.

Discussed implications for gravitino dark matter and supersymmetric particles.

Abstract

Monochromatic photons could be produced in the annihilation or decay of dark matter particles. At high energies, the search for such line features in the cosmic gamma-ray spectrum is essentially background free because plausible astrophysical processes are not expected to produce such a signal. The observation of a gamma-ray line would hence be a `smoking-gun' signature for dark matter, making the search for such signals particularly attractive. Among the different dark matter models predicting gamma-ray lines, the local supersymmetric extension of the standard model with small R-parity violation and gravitino LSP is of particular interest because it provides a framework where primordial nucleosynthesis, gravitino dark matter and thermal leptogenesis are naturally consistent. Using the two-years Fermi LAT data, we present a dedicated search for gamma-ray lines coming from dark matter annihilation or decay in the Galactic halo. Taking into account the full detector response, and using a binned profile likelihood method, we search for significant line features in the energy spectrum of the diffuse flux observed in different regions of the sky. No evidence for a line signal at the 5-sigma level is found for photon energies between 1 and 300 GeV, and conservative bounds on dark matter decay rates and annihilation cross sections are presented. Implications for gravitino dark matter in presence of small R-parity violation are discussed, as well as the impact of our results on the prospect for seeing long-lived neutralinos or staus at the LHC.