Cosmological bounds on neutrino statistics

TL;DR

This paper explores how potential violations of the Pauli exclusion principle for neutrinos could alter cosmological observations, but current data only weakly constrain neutrinos from behaving more like bosons.

Contribution

It introduces a phenomenological framework for neutrino statistics violation and assesses its impact on cosmological observables using current data.

Findings

Weak bounds on neutrino bosonic behavior from cosmology

Current data disfavors significant neutrino statistics violation

Neutrino behavior affects the evolution of the Universe in measurable ways

Abstract

We consider the phenomenological implications of the violation of the Pauli exclusion principle for neutrinos, focusing on cosmological observables such as the spectrum of Cosmic Microwave Background anisotropies, Baryon Acoustic Oscillations and the primordial abundances of light elements. Neutrinos that behave (at least partly) as bosonic particles have a modified equilibrium distribution function that implies a different influence on the evolution of the Universe that, in the case of massive neutrinos, can not be simply parametrized by a change in the effective number of neutrinos. Our results show that, despite the precision of the available cosmological data, only very weak bounds can be obtained on neutrino statistics, disfavouring a more bosonic behaviour at less than $2\sigma$.