Exploring neutrino interactions in light of present and upcoming galaxy surveys

TL;DR

This paper investigates how early universe neutrino interactions affect cosmological observations, constraining their properties using galaxy and CMB data, and forecasts future survey capabilities to improve these constraints.

Contribution

It introduces a generalized parameterization of neutrino interactions and provides combined constraints from current and future galaxy and CMB surveys.

Findings

Combined galaxy and CMB data improve constraints on neutrino free-streaming redshift.

Future surveys like Euclid significantly enhance neutrino mass and free-streaming redshift measurements.

Current data constraints are comparable to future CMB-S4 forecasts.

Abstract

In the standard cosmological framework, neutrinos begin to free-stream after the weak interaction phase ends in the early universe, at a temperature of approximately $T \sim 1 \, {\rm MeV}$. However, the onset of neutrino free-streaming can be delayed if additional interactions occur in the early universe, leaving imprints on both the cosmic microwave background (CMB) angular power spectra and the large-scale structure (LSS) matter power spectra. We present a thorough analysis of early universe neutrino interactions with a fairly generalized parameterization of the interaction rates as a power law in neutrino temperature. In this (6+2) parameter scenario, we constrain the cosmological parameters along with the free-streaming redshift and the sum of the neutrino mass in presence of such interactions, with the help of full shape (FS) galaxy power spectra from BOSS Data Release 12. Our analysis reveals that a combined dataset of FS along with CMB and BAO offers improved constraints on the free-streaming redshift from present data, comparable to the forecast results from future CMB-S4 data. Additionally, we investigate the prospects of future galaxy surveys by forecasting on Euclid mission in combination with Planck and CMB-S4, and find significant improvement on both the free-streaming redshift and the sum of the neutrino mass than the existing constraints as well as than CMB-S4 alone.