2020/08/31 by Julien Froustey, Cyril Pitrou, Maria Cristina Volpe · 3 citations
Physics and Astronomy · #Big Bang nucleosynthesis #Cosmology #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #Decoupling (probability) #Kinetic energy #Neutrino #Neutrino Physics Research #Neutrino oscillation #Nucleosynthesis #Numerical integration #Universe #astro-ph.CO #hep-ph #nucl-th
paper · pdf · doi:10.1088/1475-7516/2020/12/015
published as JCAP 12 (2020) 015 · 38 pages, 6 figures, v2: appendix discussing the effect of a CP phase. Version published in JCAP
openalex created_date 2020/08/10 · openalex publication_date 2020/12/04 · arxiv created 2020/12/06 · arxiv updated 2020/12/08 · openalex updated_date 2026/08/06
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 N eff = 3.0440. Finally we study the impact of flavour oscillations during neutrino decoupling on the subsequent primordial nucleosynthesis.