Neutrino decoupling including flavour oscillations and primordial nucleosynthesis

We revisit the decoupling of neutrinos in the early universe with flavour oscillations. We rederive the quantum kinetic equations which determine the neutrino evolution based on a BBGKY-like hierarchy, and include for the first time the full collision term, with both on- and off-diagonal terms for a...

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Bibliographic Details
Published inJournal of cosmology and astroparticle physics Vol. 2020; no. 12; p. 15
Main Authors Froustey, Julien, Pitrou, Cyril, Volpe, Maria Cristina
Format Journal Article
LanguageEnglish
Published Bristol IOP Publishing 01.12.2020
Institute of Physics (IOP)
Subjects
Chemical potential
Chemical reactions
Decoupling
Evolution
Flavor (particle physics)
High Energy Physics - Phenomenology
Kinetic equations
Mathematical analysis
Neutrinos
Nuclear fusion
Nuclear Theory
Numerical integration
Oscillations
Physics
Plasma (physics)
Quantum electrodynamics
flavor: oscillation
hierarchy
thermodynamics
neutrino: decoupling
kinetic
adiabatic
nucleosynthesis: primordial
quantum electrodynamics: correction
potential: chemical
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ISSN1475-7516
1475-7508
1475-7516
DOI10.1088/1475-7516/2020/12/015

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Summary:We revisit the decoupling of neutrinos in the early universe with flavour oscillations. We rederive the quantum kinetic equations which determine the neutrino evolution based on a BBGKY-like hierarchy, and include for the first time the full collision term, with both on- and off-diagonal terms for all relevant reactions. We focus on the case of zero chemical potential and solve these equations numerically. We also develop an approximate scheme based on the adiabatic evolution in the matter basis. In fact, the large difference between the oscillations and cosmological time scales allows to consider averaged flavour oscillations which can speed up the numerical integration by two orders of magnitude, when combined with a direct computation of the differential system Jacobian. The approximate numerical scheme is also useful to gain more insight into the physics of neutrino decoupling. Including the most recent results on plasma thermodynamics QED corrections, we update the effective number of neutrinos to Neff=3.0440. Finally we study the impact of flavour oscillations during neutrino decoupling on the subsequent primordial nucleosynthesis.
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ISSN:1475-7516
1475-7508
1475-7516
DOI:10.1088/1475-7516/2020/12/015