paper

Towards a precision calculation of in the Standard Model II: Neutrino decoupling in the presence of flavour oscillations and finite-temperature QED

arXiv:2012.02726 · doi:10.1088/1475-7516/2021/04/073

Abstract

We present in this work a new calculation of the standard-model benchmark value for the effective number of neutrinos, , that quantifies the cosmological neutrino-to-photon energy densities. The calculation takes into account neutrino flavour oscillations, finite-temperature effects in the quantum electrodynamics plasma to , where is the elementary electric charge, and a full evaluation of the neutrino--neutrino collision integral. We provide furthermore a detailed assessment of the uncertainties in the benchmark value, through testing the value's dependence on (i)~optional approximate modelling of the weak collision integrals, (ii)~measurement errors in the physical parameters of the weak sector, and (iii)~numerical convergence, particularly in relation to momentum discretisation. Our new, recommended standard-model benchmark is , where the nominal uncertainty is attributed predominantly to errors incurred in the numerical solution procedure (), augmented by measurement errors in the solar mixing angle ().

31 pages, 7 figures. Version accepted for publication in JCAP

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