Date: 03 MAY 2022 from 15:00 to 16:00
Event location: Meeting room second floor Via Irnerio 46 - In presence and online event
I will explore the possibility that theories with unstable Domain Walls in the Early Universe could be responsible for the generation of a gravitational wave background signal, focusing in particular on the recent signal detected by Pulsar Timing Arrays experiments, NANOGrav 12.5 years dataset and International PTA Data Release 2. As an example, a QCD Axion much heavier than usual could generate such a signal.
Then, I will discuss the possibility that standard QCD Axions could be produced by scatterings and decays from Standard Model particles, forming thus a Cosmic Axion Background that contributes to the abundance of relativistic relics , Neff (dark radiation). I review in various setups how this is already constrained by present experiments and how it could be observed by future CMB experiments, in particular focusing on the coupling to quarks and leptons and on the bounds on the DFSZ model.