Heavy Fermion Production and Primordial N-Spectra

Abstract

We compute the non-adiabatic production of heavy fermion during inflation due to its coupling with inflaton. The coupling, partly inspired by axion monodromy, comes from the modulation of the fermion mass by the inflaton field. Even though the fermion mass is always much higher than the Hubble scale and the density of the produced fermions is low, they can still have detectable signatures in the cosmic microwave background. Their contributions to the primordial $N$-spectra are then analyzed in detail and compared with those from the fermion's bosonic super-partner. At the classical level, where the produced particles are treated as classical sources, the effect on the $N$-spectra is proportional to the density of the produced particles and the fermion and boson cases have the same contribution. Quantum interference, however, leads to distinction between the two cases. Implications of this similarity and distinction are discussed before making general remarks about the limitations of our calculation and possible ways of overcoming them.