Seminarium "Teoria cząstek elementarnych i kosmologia"

The Standard Model (SM) leaves several fundamental questions unanswered. Traditionally, searches for new physics have focused on the TeV scale, but the lack of discoveries has motivated a shift toward exploring sub-GeV dark sectors as more viable extensions of the SM.In this context, the PTA detection of a stochastic gravitational wave background (SGWB) in the nanohertz range offers a new hint for dark sectors. In fact, one compelling explanation for this signal involves a (super)cooled first-order phase transition in a dark sector at energy scales around 100 MeVs.I will show how a spontaneously broken U(1) dark gauge symmetry can generate the observed SGWB signal and the implications for the dark sector masses and couplings. I will also discuss how the different portal couplings to the SM offer a decay possibility for the dark sector to respect the bounds from Neff.