Non-gaussianity at tree and one-loop levels from vector field perturbations

TL;DR

This paper investigates how scalar and vector field perturbations influence the primordial curvature perturbation's spectrum and bispectrum, especially considering one-loop contributions and their impact on non-gaussianity and statistical anisotropy.

Contribution

It provides a detailed analysis of tree-level and one-loop contributions from vector fields to primordial perturbations, highlighting scenarios where one-loop effects dominate and their observational implications.

Findings

One-loop contributions can dominate over tree-level in certain regimes.

High non-gaussianity levels can occur with minimal statistical anisotropy.

Potential to exceed current observational limits for non-gaussianity.

Abstract

We study the spectrum P_\zeta and bispectrum B_\zeta of the primordial curvature perturbation \zeta when the latter is generated by scalar and vector field perturbations. The tree-level and one-loop contributions from vector field perturbations are worked out considering the possibility that the one-loop contributions may be dominant over the tree level terms (both (either) in P_\zeta and (or) in B_\zeta) and viceversa. The level of non-gaussianity in the bispectrum, f_{NL}, is calculated and related to the level of statistical anisotropy in the power spectrum, g_\zeta. For very small amounts of statistical anisotropy in the power spectrum, the level of non-gaussianity may be very high, in some cases exceeding the current observational limit.