Implications of neutrino species number and summed mass measurements in cosmological observations

TL;DR

This paper explores how measurements of neutrino species number and total neutrino mass from cosmological data can inform particle physics models, including neutrino mass types and potential supersymmetry energy scales.

Contribution

It analyzes the implications of cosmological neutrino measurements for particle physics, especially regarding neutrino mass types and the potential to identify supersymmetry energy scales.

Findings

Majorana neutrinos are consistent with Planck data.

Dirac neutrinos may be viable under certain model restrictions.

Future measurements could determine neutrino mass ordering.

Abstract

We confront measurable neutrino degrees of freedom $N_{\rm eff}$ and summed neutrino mass in the early universe to particle physics at the energy scale beyond the standard model (BSM), in particular including the issue of neutrino mass type distinction. The Majorana-type of massive neutrino is perfectly acceptable by Planck observations, while the Dirac-type neutrino may survive in a restricted class of models that suppresses extra right-handed contribution to $\Delta N_{\rm eff} = N_{\rm eff} - 3$ at a nearly indistinguishable level from the Majorana case. There is a chance that supersymmetry energy scale may be identified in supersymmetric extension of left-right symmetric model if improved $N_{\rm eff}$ measurements discover a finite value. Combined analysis of this quantity with the summed neutrino mass helps to determine the neutrino mass ordering pattern, if measurement accuracy of order, $60 \sim 80\,$meV, is achieved, as in CMB-S4.