Particle production from oscillating scalar condensates

In this talk, I will discuss perturbative particle production from oscillating scalar backgrounds in a spatially flat Friedmann–Lemaître–Robertson–Walker universe using non-equilibrium quantum field theory. The latter naturally captures the thermal effects and backreaction effects. For quasi-harmonic oscillations, we adopt the multi-scale analysis to obtain analytical approximate expressions for the self-consistent evolution of the scalar background and the energy density of the produced particles in terms of the retarded self-energy and retarded proper four-vertex function, whose imaginary parts characterize different condensate decay channels and lead to dissipation. At finite temperature, there are many new condensate decay channels that would be absent at zero temperature. These new channels could play an important role in ensuring a complete reheating.