Relic neutrino freeze-out: Dependence on natural constants

Jeremiah Birrell, Cheng Tao Yang, Johann Rafelski

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Analysis of cosmic microwave background radiation fluctuations favors an effective number of neutrinos, Nν>3. This motivates a reinvestigation of the neutrino freeze-out process. Here we characterize the dependence of Nν on the Standard Model (SM) parameters that govern neutrino freeze-out. We show that Nν depends on a combination η of several natural constants characterizing the relative strength of weak interaction processes in the early Universe and on the Weinberg angle sin2 θW. We determine numerically the dependence Nν(η, sin2 θW) and discuss these results. The extensive numerical computations are made possible by two novel numerical procedures: a spectral method Boltzmann equation solver adapted to allow for strong reheating and emergent chemical non-equilibrium, and a method to evaluate Boltzmann equation collision integrals that generates a smooth integrand.

Original languageEnglish (US)
Pages (from-to)481-517
Number of pages37
JournalNuclear Physics B
StatePublished - Jan 1 2015

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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