Abstract

Warm inflation postulates an early period of sustained accelerated expansion in the presence of a thermal bath. It predicts that the inflaton fluctuations that seed structure are of classical, rather than quantum origin. The imprints of those fluctuations in the cosmic microwave background are sensitive to the functional dependence of the thermal friction coefficient that transfers energy from the inflaton to the thermal bath. An axion-like coupling between the inflaton and non-Abelian fields induces real-time sphaleron transitions which successfully source a thermal bath during inflation, providing a minimal microphysical model from which warm inflation emerges. It is known that for a pure Yang-Mills gauge group, the thermal friction has a cubic temperature dependence. In this talk, I will discuss how the presence of light fermions charged under the non-Abelian group modifies sphaleron heating. The back-reaction due to fermions leads to different functional dependencies with respect to temperature and inflaton field value, some of which have not been considered before in phenomenological studies of warm inflation. Lastly, I will comment on the prospect of Standard Model gauge interactions inducing warm inflation.