Tel Aviv University

by Edward Hardy (University of Liverpool), Wolfram Ratzinger (Weizmann Institute)

Wednesday 25 Jan 2023, 11:00 → 14:00 Asia/Jerusalem

Tel Aviv University

10:30 Coffee Break

11:00 Ed Hardy (Liverpool)

Post-inflationary ALPs: gravitational waves, targets for haloscopes, and substructure

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 dark matter substructure, which, in some cases, forms in a regime such that quantum pressure is relevant.

12:00 Lunch

13:00 Wolfram Ratzinger (Weizmann Institute)

One $\mu$ to rule them all: CMB spectral distortions can probe domain walls, cosmic strings and low scale phase transitions

I present a new probe of purely gravitationally coupled sectors with large anisotropies. These anisotropies are damped via gravitational interactions with the baryon-photon fluid, which is heated up in the process. The injected heat causes measurable distortions of the cosmic microwave background spectrum. This method can be applied to anisotropies in the form of a domain wall/cosmic string network or caused by a first order phase transition or scalar field dynamics. I show that this method can potentially probe large regions of previously unconstrained parameter space and is very much complementary to up-coming searches of gravitational waves caused by such dark sectors.