Quantum theory of fermion production after inflation
Gelfand, Daniil (Institut für Kernphysik, TU Darmstadt)

We show that quantum effects dramatically influence the production of fermions following preheating after inflation in the early universe. As a consequence fermions rapidly approach a quasi-stationary distribution with a thermal occupancy in the infrared, while the inflaton enters a turbulent scaling regime. The failure of standard semi-classical descriptions based on the Dirac equation with a homogeneous background field is caused by non-perturbatively high boson occupation numbers. During preheating the inflaton occupation number increases, thus leading to a dynamical mechanism for the enhanced production of fermions from the rescattering of the inflaton quanta. This mechanism is studied by using two-particle irreducible (2PI) effective action techniques, which we compare to results from lattice simulations.