1998/10/31 by X.R. Shi, Xiangdong Shi, George M. Fuller · 1 citation
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Big Bang nucleosynthesis #Electron #Lepton #Lepton number #Mixing (physics) #Neutrino #Neutrino Physics Research #Nuclear physics #Nuclear reaction #Nucleosynthesis #Particle physics #Particle physics theoretical and experimental studies #Physics #Quantum mechanics #astro-ph #hep-ph
paper · pdf · doi:10.1103/physrevd.59.063006
published as Phys.Rev. D59 (1999) 063006 · 20 Latex pages + 4 Figures. An appendix added. To be published in PRD
arxiv created 1998/12/21 · openalex publication_date 1999/02/17 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We discuss big bang nucleosynthesis constraints on maximal \ensuremathν_\ensuremathμ\ensuremath↔\ensuremathνs mixing. Vacuum \ensuremathν_\ensuremathμ\ensuremath↔\ensuremathνs oscillation has been proposed as one possible explanation of the Super Kamiokande atmospheric neutrino data. Based on the most recent primordial abundance measurements, we find that the effective number of neutrino species for big bang nucleosynthesis (BBN) is N_\ensuremathν\ensuremath\lesssim3.3. Assuming that all three active neutrinos are light (with masses \ensuremath≪1MeV), we examine BBN constraints on \ensuremathν_\ensuremathμ\ensuremath↔\ensuremathνs mixing in two scenarios: (1) a negligible lepton asymmetry (the standard picture) and (2) the presence of a large lepton asymmetry which has resulted from an amplification by \ensuremathν_\ensuremathτ\ensuremath↔\ensuremathν_s^\ensuremath' mixing (\ensuremathν_s^\ensuremath' being \ensuremathνs or another sterile neutrino species). The latter scenario has been proposed recently to reconcile the BBN constraints and large-angle \ensuremathν_\ensuremathμ\ensuremath↔\ensuremathνs mixing. We find that the large-angle \ensuremathν_\ensuremathμ\ensuremath↔\ensuremathνs mixing in the first scenario, which would yield N_\ensuremathν\ensuremath≈4, is ruled out as an explanation of the Super Kamiokande data. It is conceivably possible for the \ensuremathν_\ensuremathμ\ensuremath↔\ensuremathνs solution to evade BBN bounds in the second scenario, but only if 200eV2\ensuremath\lesssimm_\ensuremathν_\ensuremathτ2\ensuremath-m_\ensuremathν_s^\ensuremath'2\ensuremath\lesssim104eV2 is satisfied, and if \ensuremathν_\ensuremathτ decays non-radiatively with a lifetime \ensuremath\lesssim103yr. This mass-squared difference implies 15eV\ensuremath\lesssimm_\ensuremathν_\ensuremathτ\ensuremath\lesssim100eV if \ensuremathν_s^\ensuremath' is much lighter than \ensuremathν_\ensuremathτ. We conclude that maximal (or near maximal) \ensuremathν_\ensuremathμ\ensuremath↔\ensuremathν_\ensuremathτ mixing is a more likely explanation of the Super Kamiokande data.