Cosmological perturbations from a Spectator field during inflation

TL;DR

This paper analytically explores how a subdominant spectator field during inflation can generate large-scale perturbations, explaining CMB anisotropies with moderate non-Gaussianity and purely adiabatic features, with potential observational constraints.

Contribution

It provides a detailed analytical framework for spectator field perturbations during inflation, including higher order non-Gaussianity calculations for specific potential profiles.

Findings

Spectator field fluctuations can seed large-scale CMB anisotropies.

Perturbations are purely adiabatic due to inflaton decay dominance.

Higher order curvature perturbations are computed for different potential profiles.

Abstract

In this paper we will discuss analytically the perturbations created from a slowly rolling subdominant spectator field which decays much before the end of inflation. The quantum fluctuations of such a spectator field can seed perturbations on very large scales and explain the temperature anisotropy in the cosmic microwave background radiation with moderate non-Gaussianity, provided the relevant modes leave the Hubble patch while the spectator is slowly rolling. Furthermore, the perturbations are purely {\it adiabatic} since the inflaton decay dominates and creates all the Standard Model degrees of freedom. We will provide two examples for the spectator field potential, one with a step function profile, and the other with an inflection point. In both the cases we will compute higher order curvature perturbations, i.e.\ local bispectrum and trispectrum, which can be constrained by the forthcoming Planck data.