Beyond Standard Model Physics during Weak Decoupling

The weak decoupling epoch, roughly one second after the Big Bang, characterizes a "last scattering" of neutrinos in the hot and dense early universe where the ostensibly thermal neutrino seas both thermally decouple and chemically decouple from the electromagnetic plasma. In fact, this decoupling is not instantaneous, but rather spans a number of dynamical expansion timescales. This fact means that the weak decoupling epoch provides an interesting environment to study Beyond Standard Model (BSM) physics and its impact on the weak sector. Out of equilibrium BSM phenomena that occur around this epoch can affect the distribution of neutrinos which may have a fingerprint in cosmological observables. The next generation of cosmic microwave background observatories, of 30 meter-class telescopes, and nuclear and neutrino laboratory experiments provide an interesting possibility of probing BSM physics through the interplay of such physics with neutrinos and of neutrinos with cosmological observables.