Exact thermalization mechanism after inflaton decay

Determine the microphysical thermalization mechanism by which the decay products of the inflaton field achieve thermal equilibrium and establish the radiation-dominated hot Big Bang plasma at the end of reheating, including the relevant scattering processes, timescales, and conditions under typical inflaton–matter couplings.

Background

In the non-perturbative reheating picture, the post-inflationary evolution proceeds through preheating (parametric resonance), backreaction/fragmentation of the inflaton condensate, and finally a stage of scattering and thermalization. While the early stages can be modeled semi-analytically and via lattice simulations, the detailed microphysics that leads to a fully thermalized radiation bath remains uncertain.

Establishing the thermalization pathway is crucial for connecting inflation to the standard hot Big Bang, fixing the reheating temperature, and ensuring consistency with Big Bang Nucleosynthesis. It also impacts predictions for relics such as gravitational waves, primordial black holes, and the early-time equation of state.