Speaker
Description
In standard cosmological models, dark matter (DM) overdensities known as prompt cusps can form in the early Universe, persisting through cosmic time. Unlike resolved DM substructures, these dense cusps produce an annihilation flux that scales linearly with the DM density, $\rho$, rather than $\rho^2$. This results in an extended, yet bright, annihilation signal from massive structures such as galaxy clusters. In this work, we use 15 years of Fermi-LAT data to search for gamma-ray signatures from seven nearby galaxy clusters. Finding no significant excess, we set the strongest existing limits on WIMP DM annihilation from cluster-scale prompt cusps, ruling out the thermal relic cross-section for DM masses up to ~200 GeV. These constraints exceed those from dwarf spheroidal galaxies and the isotropic gamma-ray background, providing a robust test of DM models. Our findings highlight the power of galaxy clusters as probes of annihilating DM and underscore the need for dedicated observational strategies targeting these extended structures in future gamma-ray observations. Additionally, we provide an overview of the expected sensitivity of the Cherenkov Telescope Array (CTA) to these annihilation signals, demonstrating its potential to extend current constraints to higher masses and fainter DM annihilation rates.
