Primordial neutrinos and new physics: novel approach to solving neutrino Boltzmann equation

TL;DR

This paper introduces a novel, efficient method to solve the neutrino Boltzmann equation, clarifying the impact of new physics on cosmic neutrino behavior during decoupling, with implications for cosmological observations.

Contribution

A new comprehensive approach to solving the neutrino Boltzmann equation that addresses previous model-dependence and computational inefficiencies.

Findings

Resolved discrepancies about non-thermal neutrinos' impact on N_eff

Provided insights into decaying new physics particles on MeV plasma

Enhanced understanding of neutrino dynamics during decoupling

Abstract

Understanding how new physics influences the dynamics of cosmic neutrinos during their decoupling is crucial in light of upcoming precise cosmological observations and the need to reconcile cosmological and laboratory probes. Existing approaches to solving the neutrino Boltzmann equation are often model-dependent, computationally inefficient, and yield contradictory results. To solve this problem, we introduce a novel method to comprehensively study neutrino dynamics. We apply this method to several case studies, resolving the discrepancy in the literature about the impact of non-thermal neutrinos on $N_{\rm eff}$ and providing important insights about the role of decaying new physics particles on MeV plasma.