Inflationary particle production and implications for WIMP substructure

I explore the observational consequences of resonant particle production during inflation, focusing on its impact on dark matter annihilation signals today. A transient burst of particle production generates localized features in the primordial power spectrum, enhancing the formation of compact small-scale dark matter structures known as prompt cusps. If dark matter consists of thermal weakly interacting massive particles, the resulting small-scale structures substantially boost annihilation rates, leaving potentially detectable imprints in gamma-ray observations. Using 15 years of Fermi Large Area Telescope data targeting the Virgo cluster, I derive upper limits on the thermally averaged annihilation cross section ⟨ σ v ⟩ , connecting inflationary particle production in the early Universe with present-day observations constraining dark matter annihilation.