Dissipation of oscillating scalar backgrounds in an FLRW universe

Abstract

We study particle production from oscillating scalar backgrounds in a spatially flat Friedmann-Lemaître-Robertson-Walker universe using non-equilibrium quantum field theory which fully captures the thermal effects and backreaction effects. To be concrete, we consider a Z 2 -symmetric two-scalar model with quartic interactions. 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. We find that reheating in this model can be complete if the imaginary part of the retarded self-energy is non-vanishing, which causes dissipation only at finite temperature through Landau damping. Our results can be generalized to more complicated models and thus could provide a general framework for studying the perturbative reheating process in the early Universe or perturbative production of Dark Matter from an oscillating inflaton.

On gravitational preheating

“…Since all of our operators are Planck-suppressed, such processes are slower than the Hubble rate and thus do not lead to inflaton thermalization [34] nor significant DM production. 4 At weak couplings, the inflaton field may remain semi-classical during reheating, in which case the effects of the SM thermal bath can be included along the lines of [35,36].…”

Fate of oscillating homogeneous ℤ2-symmetric scalar condensates in the early Universe

“…This is crucial because it leads to a conclusion different from that given in refs. [43,44]. If one uses the high-temperature approximation, it is possible to have a decay rate that is always larger than the Hubble parameter, and one may conclude that the condensate can transfer all its energy to radiation for some values of the coupling and mass parameters.…”

“…Properly truncating the effective action and taking into account the homogeneity of the condensate and plasma, one obtains the condensate EoM as [36,44]…”

“…By treating the remaining terms as perturbations, one can solve the condensate EoM using multiple-scale analysis [34,35] as described in refs. [36,44]. There, constant temperature and M ϕ are assumed.…”

On gravitational preheating

“…Since all of our operators are Plancksuppressed, such processes are slower than the Hubble rate and thus do not lead to inflaton thermalization [31] nor significant DM production. At weak couplings, the inflaton field may remain semi-classical during reheating, in which case the effects of the SM thermal bath can be included along the lines of [32], [33].…”