Dark Matter via Inverse Phase Transition: going beyond freeze-in with observable Gravitational Waves

by Prof. Alex Vikman

Thursday 9 Jun 2022, 12:00 → 14:00 Europe/Madrid

IFAE Seminar Room + Zoom (Hybrid)

I will discuss a recently proposed class of models where Dark Matter (DM) is produced via an inverse phase transition. The inverse phase transition can be caused by coupling to some cosmological field. For instance, this field can be the Ricci scalar, as in e-Print: 2004.03410; primordial magnetic field, as in e-Print: 2010.03383; or thermal fluctuations of other fields, as in e-Print: 2104.13722. In this most recent work we proposed a novel scenario of DM production tidy connected with generation of gravitational waves. DM is modelled as a real scalar, which interacts with the hot primordial plasma through a portal coupling to another scalar field. For a particular sign of the coupling, this system exhibits an inverse phase transition. The latter leads to an abundant DM production, even if the portal interaction is so weak that the freeze-in mechanism is inefficient. The model predicts domain wall formation in the early Universe, long before the inverse phase transition. These domain walls have a tension decreasing with time, and completely disappear at the inverse phase transition, so that the problem of overclosing the Universe is avoided. The domain wall network emits gravitational waves with characteristics defined by those of DM. In particular, the peak frequency of gravitational waves is determined by the portal coupling constant, and falls in the observable range of currently planned gravitational wave detectors.