Speaker
Purusottam Ghosh
(IMSc Chennai)
Description
The precise measurement of $N_{\rm eff}$ at the time of cosmic microwave background (CMB) formation by Planck (2018) can be used to understand the new fundamental interactions, in particular those involving light mediators. In this talk, I will discuss the impact of light gauge bosons (order of MeV) originating from various types of $U(1)_X$ on the $N_{\rm eff}$. In the low-mass region, the bound on $N_{\rm eff}$ at CMB is more stringent than current experimental constraints.
