Cosmological bounds on neutrino degeneracy improved by flavor oscillations

By A. Dolgov, S. Hansen, S. Pastor, S. Petcov, G. Raffelt, D. V. Semikoz. 2002

305 citations recorded by the source corpus.

Abstract We study three-flavor neutrino oscillations in the early universe in the presence of neutrino chemical potentials. We take into account all effects from the background medium, i.e., collisional damping, the refractive effects from charged leptons, and in particular neutrino self-interactions that synchronize the neutrino oscillations. We find that effective flavor equilibrium between all active neutrino species is established well before the big-bang nucleosynthesis (BBN) epoch if the neutrino oscillation parameters are in the range indicated by the atmospheric neutrino data and by the large mixing angle (LMA) MSW solution of the solar neutrino problem. For the other solutions of the solar neutrino problem, partial flavor equilibrium may be achieved if the angle θ13 is close to the experimental limit tan2θ13≲0.065. In the LMA case, the BBN limit on the νe degeneracy parameter, |ξν|≲0.07, now applies to all flavors. Therefore, a putative extra cosmic radiation contribution from degenerate neutrinos is limited to such low values that it is neither observable in the large-scale structure of the universe nor in the anisotropies of the cosmic microwave background radiation. Existing limits and possible future measurements, for example in KATRIN, of the absolute neutrino mass scale will provide unambiguous information on the cosmic neutrino mass density, essentially free of the uncertainty of the neutrino chemical potentials.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/e845fd8d8ddbc21c637c4c48ff14d009076a59e5

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Citations in the corpus

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Neutrino Mass from Cosmology (2012, methodology): “in [26, 27, 28] that this is the case for the neutrino mixing parameters in the region favoured by present data.”
Neutrino decoupling beyond the Standard Model: CMB constraints on the Dark Matter mass with a fast and precise Neff evaluation (2018, background): “Furthermore, given the observed pattern of masses and mixings [40–42] the neutrino oscillations become active in the early Universe for temperatures T = 3− 5 MeV [43, 44] (see Appendix A.”
Self-induced conversion in dense neutrino gases: Pendulum in flavour space (2006, background): “Various qualitative and quantitative aspects of synchronised oscillations and applications to neutrino flavour oscillations in the early universe [18, 19, 20, 21] were studied a few years ago, motivated by the question if neutrinos with chemical potentials reach flavour equilibrium in the early univ”
Cosmology with a very light Lμ − Lτ gauge boson (2019, background): “After neutrino decoupling, neutrino oscillations are efficient enough to approximately equilibrate the neutrino distributions [49–51], and thus even if the Z ′ only interacts with muon and tau neutrinos the rapid oscillation will render the νe distribution very similar to that of νμ and ντ .”
Precision early universe thermodynamics made simple: Neff and neutrino decoupling in the Standard Model and beyond (2020, background): “Neutrino oscillations are active at the time of neutrino decoupling [28, 29, 43, 44].”
Sterile neutrinos in cosmology (2017, background): “but asymmetries can produce interesting collective effects [90, 91, 92].”