Gamma-rays from Nearby Clusters: Constraints on Selected Decaying Dark Matter Models

TL;DR

This paper investigates gamma-ray constraints on two decaying dark matter models using Fermi-LAT data, finding that GUT-scale decaying dark matter is largely disfavored but can still explain PAMELA positron excess, while R-parity violating gravitino models face weaker constraints.

Contribution

It provides the first detailed gamma-ray constraints on specific decaying dark matter models accounting for cosmic-ray excesses, highlighting tensions and viability.

Findings

GUT decaying dark matter is disfavored by gamma-ray constraints from galaxy clusters.

R-parity violating gravitino dark matter faces weaker gamma-ray constraints.

Some tension exists between gamma-ray limits and cosmic-ray excess explanations.

Abstract

Recently, the Fermi-LAT collaboration reported upper limits on the GeV gamma-ray flux from nearby clusters of galaxies. Motivated by these limits, we study corresponding constraints on gamma-ray emissions from two specific decaying dark matter models, one via grand unification scale suppressed operators and the other via R-parity violating operators. Both can account for the PAMELA and Fermi-LAT excesses of e^\pm. For GUT decaying dark matter, the gamma-rays from the M49 and Fornax clusters, with energy in the range of 1 to 10 GeV, lead to the most stringent constraints to date. As a result, this dark matter is disfavored with conventional model of e^\pm background. In addition, it is likely that some tension exists between the Fermi-LAT e^\pm excess and the gamma ray constraints for any decaying dark matter model, provided conventional model of e^\pm background is adopted. Nevertheless, the GUT decaying dark matter can still solely account for the PAMELA positron fraction excess without violating the gamma-ray constraints. For the gravitino dark matter model with R-parity violation, cluster observations do not give tight constraints. This is because a different e^\pm background has been adopted which leads to relatively light dark matter mass around 200 GeV.