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Non-Gaussianities in models with a varying inflaton decay rate

Matias Zaldarriaga

TL;DR

This work analyzes primordial non-Gaussianities in models where density perturbations originate from spatial variations in the inflaton decay rate Γ during reheating. The authors demonstrate that generated non-Gaussianities are of the local type, with $R = R_g + f_{NL} (R_g^2 - ⟨R_g^2⟩)$, because perturbations originate outside the horizon and are imprinted during reheating. They identify two main sources of non-Gaussianity: non-linearities in the Γ→R mapping and non-Gaussian intrinsic fluctuations of the fluctuating field δφ, including cases with Gaussian δφ and cases with non-quadratic potentials. Depending on model details, such as the efficiency of the Γ-controlled perturbation and the presence of self-interactions, $f_{NL}$ can be of order a few to tens, offering potential observability with future CMB and large-scale structure probes, while remaining compatible with current constraints.

Abstract

We consider the expected level of primordial non-Gaussianities in models in which density perturbations are produced by spatial fluctuations in the decay rate of the inflaton. We consider both the non-Gaussianities resulting from the self-couplings of the field that controls the decay rate as well as from the non-linear relation between field and curvature perturbations. We show that in these scenario non-Gaussianities are of the "local" form, that is well described be the ansatz R =Rg + f_{NL} (Rg^2 - <Rg^2>). This is a consequence of the fact that they were created when modes were already outside the horizon. We show that f_{NL} is naturally of order a few in these models, much larger than what is expected in the standard one field models of inflation (f_{NL}\sim 10^{-2}) and possibly accessible to observations.

Non-Gaussianities in models with a varying inflaton decay rate

TL;DR

This work analyzes primordial non-Gaussianities in models where density perturbations originate from spatial variations in the inflaton decay rate Γ during reheating. The authors demonstrate that generated non-Gaussianities are of the local type, with , because perturbations originate outside the horizon and are imprinted during reheating. They identify two main sources of non-Gaussianity: non-linearities in the Γ→R mapping and non-Gaussian intrinsic fluctuations of the fluctuating field δφ, including cases with Gaussian δφ and cases with non-quadratic potentials. Depending on model details, such as the efficiency of the Γ-controlled perturbation and the presence of self-interactions, can be of order a few to tens, offering potential observability with future CMB and large-scale structure probes, while remaining compatible with current constraints.

Abstract

We consider the expected level of primordial non-Gaussianities in models in which density perturbations are produced by spatial fluctuations in the decay rate of the inflaton. We consider both the non-Gaussianities resulting from the self-couplings of the field that controls the decay rate as well as from the non-linear relation between field and curvature perturbations. We show that in these scenario non-Gaussianities are of the "local" form, that is well described be the ansatz R =Rg + f_{NL} (Rg^2 - <Rg^2>). This is a consequence of the fact that they were created when modes were already outside the horizon. We show that f_{NL} is naturally of order a few in these models, much larger than what is expected in the standard one field models of inflation (f_{NL}\sim 10^{-2}) and possibly accessible to observations.

Paper Structure

This paper contains 6 sections, 36 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Density perturbations in the new scenario
  3. Non-Gaussianities
  4. Gaussian $\delta \phi_i$ fluctuations
  5. non-Gaussian $\delta \phi_i$ fluctuations
  6. Summary

Figures (1)

  • Figure 1: Expansion factor normalization $g$ as a function of $\Gamma/H$ after reheating. The curve was obtained by solving equations (\ref{['evoleq']}) numerically starting with $\epsilon_r=0$ and Hubble expansion $H$ at the initial time.