Probing Dark Matter Decay and Annihilation with Fermi LAT Observations of Nearby Galaxy Clusters

TL;DR

This study uses three years of Fermi LAT gamma-ray data to search for dark matter decay or annihilation signals in nearby galaxy clusters, setting limits on dark matter properties and implications for particle physics.

Contribution

It provides new constraints on dark matter decay and annihilation in galaxy clusters, considering uncertainties and substructures, and compares these limits with extragalactic gamma-ray background constraints.

Findings

No significant gamma-ray emission detected from clusters.

Cluster limits on dark matter decay are competitive below a few hundred GeV.

Leptonic decay limits are stronger than extragalactic background limits across all masses.

Abstract

Galaxy clusters are promising targets for indirect dark matter searches. Gamma-ray signatures from the decay or annihilation of dark matter particles inside these clusters could be observable with the Fermi Large Area Telescope (LAT). Based on three years of Fermi LAT gamma-ray data, we analyze the flux coming from eight nearby clusters individually as well as in a combined likelihood analysis. Concentrating mostly on signals from dark matter decay, we take into account uncertainties of the cluster masses as determined by X-ray observations and model the cluster emission as extended sources. Searching for different hadronic and leptonic decay and annihilation spectra, we do not find significant emission from any of the considered clusters and present limits on the dark matter lifetime and annihilation cross-section. We compare our lifetime limits derived from cluster observations with the limits that can be obtained from the extragalactic gamma-ray background (EGBG), and find that in case of hadronic decay the cluster limits become competitive at dark matter masses below a few hundred GeV. In case of leptonic decay, however, galaxy cluster limits are stronger than the limits from the EGBG over the full considered mass range. Finally, we show that in presence of dark matter substructures down to 10^-6 solar masses the limits on the dark matter annihilation cross-section could improve by a factor of a few hundred, possibly going down to the thermal cross-section of 3 10^-26 cm^3 s^-1 for dark matter masses < 150 GeV and annihilation into $b\bar{b}$. As a direct application of our results, we derive limits on the lifetime of gravitino dark matter in scenarios with R-parity violation. Implications of these limits for the possible observation of long-lived superparticles at the LHC are discussed.