Influence of reheating on the trispectrum and its scale dependence

Abstract

We study the evolution of the non-linear curvature perturbation during perturbative reheating, and hence how observables evolve to their final values which we may compare against observations. Our study includes the evolution of the two trispectrum parameters, gNL and τNL, as well as the scale dependence of both fNL and τNL. In general the evolution is significant and must be taken into account, which means that models of multifield inflation cannot be compared to observations without specifying how the subsequent reheating takes place. If the trispectrum is large at the end of inflation, it normally remains large at the end of reheating. In the classes of models we study, it remains very hard to generate τNL f 2 NL , regardless of the decay rates of the fields. Similarly, for the classes of models in which gNL τNL during slow-roll inflation, we find the relation typically remains valid during reheating. Therefore it is possible to observationally test such classes of models without specifying the parameters of reheating, even though the individual observables are sensitive to the details of reheating. It is hard to generate an observably large gNL however. The runnings, n f NL and nτ NL , tend to satisfy a consistency relation nτ NL = (3/2)n f NL regardless of the reheating timescale, but are in general too small to be observed for the class of models considered.

A critical review of classical bouncing cosmologies

“…It should be noted that predictions for non-linearity parameters can change by factors of order one during (p)reheating if an adiabatic regime has not been reached previously [439,440]; that non-gaussianities are subject to change and often transient as long as the adiabatic regime is not reached was pointed out in [428,441] see also [442] for subsequent work. A turn in field space may arise due to the ekpyrotic potential: as the fields need to follow the ridge of the potential in order to yield a scale-invariant spectrum, see Sec.…”

Effect of reheating on predictions following multiple-field inflation

“…For two-field inflation, numerical studies [29,37,38] have demonstrated that observables such as the power spectrum P(k), and the local shape bispectrum parameter f NL can be very sensitive to the details of reheating. This sensitivity was quantified in Ref.…”

Multifield reheating after modular j-inflation

“…In the context of multifield theories the analysis becomes complicated and most work has been restricted to separable potentials [16,17,18,19,20,21,22], but interacting fields have been considered for flat target spaces in refs. [23,24,25], and a discussion admitting curved inflaton targets can be found in ref. [26,27].…”