HIDDeN & ASYMMETRY WEBINAR: Tuesday March 7th, 2023 @16:00 (CET)
Speaker: Marco Gorghetto (Weizmann Institute)
Title: Post-inflationary axions: gravitational waves, targets for haloscopes, and substructure
Abstract: If the Peccei-Quinn symmetry associated to an axion-like particle has ever been restored after inflation, axion strings and domain walls inevitably form. I will argue that these topological defects can have interesting experimental and observational consequences. In particular, if the axion decay constant is larger than 10^14 GeV, the strings produce an observable stochastic gravitational wave background. In other theories, the contribution to the relic abundance from domain walls allows an axion with a relatively small decay constant, and therefore a possibly large coupling to photons, to comprise the full dark matter abundance. The relic axions are produced with a spatial distribution that might lead to the formation of dark matter small-scale structure, which, in some cases, forms in a regime such that quantum pressure is relevant.