Speaker
Description
Explaining the large amplitude of the nano-Hertz stochastic gravitational-wave background observed by pulsar timing arrays (PTAs) typically requires extremely energetic primordial sources. Such mechanisms generically produce large curvature perturbations, which subsequently collapse into ultra-compact mini-halos (UCMHs). If
dark matter consists of weakly interacting massive particles (WIMPs), the high densities inside UCMHs lead to efficient dark-matter annihilation, generating potentially observable photon and neutrino fluxes. I will show that, for several proposed primordial explanations of the PTA signal, including curvature-peak scenarios, first-order
phase transitions, and domain-wall dynamics, the predicted fluxes from the resulting UCMH population exceed current observational bounds. These results therefore place strong tension between WIMP dark matter and new-physics interpretations of the PTA signal.
