Dark Radiation and Inflationary Freedom

TL;DR

This paper explores how non-standard primordial power spectra from inflation can alter dark radiation constraints, potentially favoring light sterile neutrinos and relaxing axion mass bounds based on cosmological data.

Contribution

It demonstrates that relaxing the standard PPS assumption can significantly change dark radiation constraints from CMB and cosmological observations.

Findings

Non-standard PPS can favor thermalized sterile neutrinos.

Constraints on axion mass are relaxed with non-standard PPS.

Inflationary freedom impacts dark radiation bounds.

Abstract

A relaxed primordial power spectrum (PPS) of scalar perturbations arising from inflation can impact the dark radiation constraints obtained from Cosmic Microwave Background and other cosmological measurements. If inflation produces a non-standard PPS for the initial fluctuations, a fully thermalized light sterile neutrino can be favoured by CMB observations, instead of being strongly disfavoured. In the case of a thermal axion, the constraints on the axion mass are relaxed when the PPS is different from the standard power law.