Light Sterile Neutrinos and Inflationary Freedom

TL;DR

This paper explores how allowing flexible primordial power spectra can reconcile the existence of eV-scale sterile neutrinos with cosmological data, revealing a feature around a specific wavenumber.

Contribution

It introduces a method to analyze cosmological data with a non-standard primordial power spectrum shape, accommodating sterile neutrinos.

Findings

Reconciliation of sterile neutrinos with cosmological data.

Identification of a feature in the primordial power spectrum.

Flexibility in the primordial spectrum shape impacts neutrino constraints.

Abstract

We perform a cosmological analysis in which we allow the primordial power spectrum of scalar perturbations to assume a shape that is different from the usual power-law predicted by the simplest models of cosmological inflation. We parameterize the free primordial power spectrum with a "piecewise cubic Hermite interpolating polynomial" (PCHIP). We consider a 3+1 neutrino mixing model with a sterile neutrino having a mass at the eV scale, which can explain the anomalies observed in short-baseline neutrino oscillation experiments. We find that the freedom of the primordial power spectrum allows to reconcile the cosmological data with a fully thermalized sterile neutrino in the early Universe. Moreover, the cosmological analysis gives us some information on the shape of the primordial power spectrum, which presents a feature around the wavenumber $k=0.002\,\text{Mpc}^{-1}$.