Gravity, Parametric Resonance and Chaotic Inflation

For nearly a decade it has been known that coherent processes at the end of inflation can drive explosive particle production [1] via parametric resonance, leading to an era of preheating in the post-inflationary universe. Earlier assumptions about the transfer of energy from the inflaton to “regular” matter have been overturned, and the phenomenology of the post-inflationary universe is thus much richer than previously suspected. However, the corollary of such interesting behavior is understanding preheating has been a long and arduous task [2–14,17,15,16,18–27]. In particular, the problem is intrinsically nonlinear and takes place far from thermal equilibrium. Moreover, employing simplifying assumptions that are often useful in other circumstances can suppress crucial features of the preheating era, and when they are discarded the resulting predictions can change dramatically. The simplest model to exhibit parametric resonance is chaotic inflation driven by the quartic potential,