Classical non-Gaussianity from non-linear evolution of curvature perturbations

TL;DR

This paper investigates how non-linear evolution during the matter-dominated era induces classical non-Gaussian features in curvature perturbations, affecting the bispectrum on different scales and providing potential tests of general relativity.

Contribution

It provides an exact quantification of classical non-linear effects on curvature perturbations and their impact on the bispectrum across super- and sub-horizon scales.

Findings

Super-horizon bispectrum peaks with specific f_NL values.

Sub-horizon bispectrum exhibits equilateral shape.

Classical non-linear evolution can serve as a probe of general relativity.

Abstract

We study the non-linear evolution of the curvature perturbations during matter dominated era. We show that regardless of the origin of the primordial perturbation, the Bardeen potential and curvature receive sizable contributions from the classical non-linear evolution effects, and quantify them exactly. On the super-horizon scales we have squeezed peak of the bispectrum with magnitude, in terms of the local non-linear parameters of Bardeen curvature, 1/6 < f_{NL} 19/15, and of Bardeen potential, -1/4 < f_{NL} < 7/5, depending on the configuration of momenta. On the sub-horizon scales the bispectrum show equilateral shape, and can serve as a potential probe of general relativity.