Higher order spectra from an initially anisotropic universe

TL;DR

This paper analyzes higher order spectra of a scalar field in an initially anisotropic universe, revealing unique features in the bispectrum and trispectrum caused by primordial anisotropy and negative frequency modes.

Contribution

It introduces the calculation of higher order spectra in an anisotropic universe, including planar modes and effects of negative frequency modes, highlighting new features in trispectra.

Findings

Distinct features in the bispectrum due to anisotropy

Richer trispectrum structures from primordial anisotropy

Effects of negative frequency modes on spectra

Abstract

In this paper, we present the higher order spectra of a scalar field produced through the higher derivative interactions in the initially anisotropic universe. Although we ignore the backreaction of the scalar field on the geometry, our analysis should have much overlap with the quantum fluctuations of the inflaton field in the anisotropic universe. We also include the planar modes whose momenta are along the plane which is perpendicular to the primordial preferred direction, for which effects of the initial anisotropy are not suppressed. The presence of a negative frequency mode produces features distinguishable from the case of the de Sitter inflation. We also show that richer features appear in the trispectra due to the primordial anisotropy.