Scalar perturbations in conformal rolling scenario with intermediate stage

TL;DR

This paper explores how an intermediate stage in a conformal rolling cosmological scenario affects scalar perturbations, leading to distinctive features like negative tilt, statistical anisotropy, and unique non-Gaussianity.

Contribution

It introduces a model with a long intermediate stage between conformal rolling and horizon exit, revealing novel effects on scalar perturbations not previously studied.

Findings

Negative scalar tilt induced by the intermediate stage

Statistical anisotropy in all even multipoles, starting from quadrupole

Presence of a peculiar form of non-Gaussianity

Abstract

Scalar cosmological perturbations with nearly flat power spectrum may originate from perturbations of the phase of a scalar field conformally coupled to gravity and rolling down negative quartic potential. We consider a version of this scenario whose specific property is a long intermediate stage between the end of conformal rolling and horizon exit of the phase perturbations. Such a stage is natural, e.g., in cosmologies with ekpyrosis or genesis. Its existence results in small negative scalar tilt, statistical anisotropy of all even multipoles starting from quardupole of general structure (in contrast to the usually discussed single quadrupole of special type) and non-Gaussianity of a peculiar form.