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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mo stretchy="false">⟨</a:mo> <a:mi>σ</a:mi> <a:mi>v</a:mi> <a:mo stretchy="false">⟩</a:mo> </a:math> , connecting inflationary particle production in the early Universe with present-day observations constraining dark matter annihilation.