Relic Neutrino Freeze-out: Dependence on Natural Constants

Jeremiah Birrell; Cheng-Tao Yang; Johann Rafelski

doi:10.1016/j.nuclphysb.2014.11.020

paper

Relic Neutrino Freeze-out: Dependence on Natural Constants

arXiv:1406.1759 · doi:10.1016/j.nuclphysb.2014.11.020

Abstract

Analysis of cosmic microwave background radiation fluctuations favors an effective number of neutrinos, $N_{ν} > 3$ . This motivates a reinvestigation of the neutrino freeze-out process. Here we characterize the dependence of $N_{ν}$ on the Standard Model (SM) parameters that govern neutrino freeze-out. We show that $N_{ν}$ 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 $sin^{2} θ_{W}$ . We determine numerically the dependence $N_{ν} (η, sin^{2} θ_{W})$ 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 emerging chemical non-equilibrium, and a method to evaluate Boltzmann equation collision integrals that generates a smooth integrand.

38 pages, 14 figures

Relic Neutrino Freeze-out: Dependence on Natural Constants

Abstract

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