Limits on Dark Matter Annihilation Signals from the Fermi LAT 4-year Measurement of the Isotropic Gamma-Ray Background

TL;DR

This study uses 4-year Fermi LAT gamma-ray data to search for dark matter annihilation signals in the isotropic gamma-ray background, setting new limits on WIMP models up to tens of TeV.

Contribution

It provides an improved theoretical framework for predicting cosmological dark matter signals and sets the strongest constraints to date on dark matter annihilation at TeV energies.

Findings

No evidence of dark matter signals was found.

The limits on dark matter annihilation are the most stringent at TeV energies from Fermi LAT data.

The analysis extends the energy range of the IGRB measurement up to 820 GeV.

Abstract

We search for evidence of dark matter (DM) annihilation in the isotropic gamma-ray background (IGRB) measured with 50 months of Fermi Large Area Telescope (LAT) observations. An improved theoretical description of the cosmological DM annihilation signal, based on two complementary techniques and assuming generic weakly interacting massive particle (WIMP) properties, renders more precise predictions compared to previous work. More specifically, we estimate the cosmologically-induced gamma-ray intensity to have an uncertainty of a factor ~20 in canonical setups. We consistently include both the Galactic and extragalactic signals under the same theoretical framework, and study the impact of the former on the IGRB spectrum derivation. We find no evidence for a DM signal and we set limits on the DM-induced isotropic gamma-ray signal. Our limits are competitive for DM particle masses up to tens of TeV and, indeed, are the strongest limits derived from Fermi LAT data at TeV energies. This is possible thanks to the new Fermi LAT IGRB measurement, which now extends up to an energy of 820 GeV. We quantify uncertainties in detail and show the potential this type of search offers for testing the WIMP paradigm with a complementary and truly cosmological probe of DM particle signals.