Spinning Cosmology

We study the signatures left by new light particles with spin on the primordial cosmological fluctuations.
In de Sitter spacetime there is a lower bound on non-zero mass of the fields with spin known as Higuchi bound. It forces the fluctuations of such fields to decay on super-horizon scales and causes their contribution to the correlation functions to be highly suppressed. We show that the inflationary backgrounds do allow for spinning particles that are parametrically lighter than the expansion rate. I introduce the description of the particles with spin in the context of the Effective Field Theory of Inflation and discuss the main signatures left by such particles on the primordial fluctuations.