The Origin of Matter in the Universe: Reheating after Inflation

TL;DR

The paper analyzes how the Universe transitions from inflation to the hot Big Bang through reheating, highlighting both perturbative decay and nonperturbative dynamics. It introduces a quantum-field-theoretic treatment in a time-dependent background, showing that inflaton energy is rapidly transferred to bosons via broad parametric resonance (preheating), producing highly nonthermal occupation numbers and triggering backreaction. The work identifies a sequence of stages—preheating, narrower-resonance decay, and thermalization—and demonstrates that non-thermal, large-amplitude fluctuations can drive phase transitions and defect formation long before thermal equilibrium is reached. These findings have important implications for baryogenesis, topological defect production, and the overall thermal history of the early Universe, expanding the inflationary model space beyond perturbative reheating.

Abstract

In the inflationary scenario all the matter constituting the universe was created from the process of reheating after inflation. Recent development of the theory of reheating is briefly reviewed. The list of topics includes elementary (perturbative) theory of reheating; quantum field theory in a time-varying background; parametric resonance and explosive particle creation; non-thermal phase transitions from reheating; baryogenesis from reheating; residual oscillations of the scalar field, and other cosmological applications.