Abstract
Light fields with spatially varying backgrounds can modulate cosmic preheating, and imprint the nonlinear effects of preheating dynamics at tiny scales on large scale fluctuations. This provides us a unique probe into the preheating era which we dub the “cosmic microscope”. We identify a distinctive effect of preheating on scalar perturbations that turns the Gaussian primordial fluctuations of a light scalar field into square waves, like a diode. The effect manifests itself as local non-Gaussianity. We present a model, “modulated partial preheating”, where this nonlinear effect is consistent with current observations and can be reached by near future cosmic probes.
Highlights
In this paper we have studied a scenario of modulated partial preheating, in which the space variation of a modulating field χ triggers the preheating of a spectator field σ after inflation
This provides a unique chance to observe the nonlinear dynamics of preheating era which is in general difficult to probe directly
We have showed that the expansion histories of local patches during preheating have a two-phase structure controlled by the background value of the modulating field χ: the patches with |χ| larger than a critical value χc have efficient particle production, while patches with |χ| < χc do not
Summary
One needs a mechanism to stop inflation and convert the inflaton energy to thermal radiation. Varying χ over large scales induces a change of expansion histories across different Hubble patches, and provides a new source generating curvature perturbations. This is known as the modulated reheating scenario, and we call χ the modulating field on. Instead of the perturbative decay rate Γ, the preheating efficiency is controlled by the μk parameter introduced in eq (2.4), which depends on the coupling g, and on the modulating field χ, in a highly nonlinear way, as illustrated in figure 2. We will show that the curvature perturbation induced by such a modulated preheating scenario is almost always too large to be consistent with the observed value ζ ∼ 10−5.
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