Minimal Preheating

An oscillating inflaton field induces small amplitude oscillations of the Hubble parameter at the end of inflation. These Hubble parameter induced oscillations, in turn, trigger parametric particle production of all light fields, even if they are not directly coupled to the inflaton. We here study the induced particle production for a light scalar field (e.g. the Standard Model Higgs field) after inflation as a consequence of this effect. Our analysis yields a model-independent lower bound on the efficiency of energy transfer from the inflaton condensate to particle excitations.