Neutrino-mixing-generated lepton asymmetry and the primordial 4He abundance
Abstract
It has been proposed that an asymmetry in the electron neutrino sector may be generated by resonant active-sterile neutrino transformations during big bang nucleosynthesis (BBN). We calculate the change in the primordial 4He yield Y resulting from this asymmetry, taking into account both the time evolution of the νe and ν¯e distribution function and the spectral distortions in these. We calculate this change in two schemes: (1) a lepton asymmetry directly generated by νe mixing with a lighter right-handed sterile neutrino νs, and (2) a lepton asymmetry generated by a ντ<-->νs or νμ<-->νs transformation which is subsequently partially converted to an asymmetry in the νeν¯e sector by a matter-enhanced active-active neutrino transformation. In the first scheme, we find that the percentage change in Y is between -1% and 9% (with the sign depending on the sign of the asymmetry), bounded by the Majorana mass limit mνe<~1 eV. In the second scheme, the maximal percentage reduction in Y is 2%, if the lepton number asymmetry in neutrinos is positive; otherwise, the percentage increase in Y is <~5% for m2νμ,ντ-m2νs<~104 eV. We conclude that the change in the primordial 4He yield induced by a neutrino-mixing-generated lepton number asymmetry can be substantial in the upward direction, but limited in the downward direction.
- Publication:
-
Physical Review D
- Pub Date:
- September 1999
- DOI:
- 10.1103/PhysRevD.60.063002
- arXiv:
- arXiv:astro-ph/9905259
- Bibcode:
- 1999PhRvD..60f3002S
- Keywords:
-
- 14.60.Pq;
- 14.60.St;
- 26.35.+c;
- 95.30.Cq;
- Neutrino mass and mixing;
- Non-standard-model neutrinos right-handed neutrinos etc.;
- Big Bang nucleosynthesis;
- Elementary particle processes;
- Astrophysics;
- High Energy Physics - Phenomenology
- E-Print:
- 15 pages, 7 figures, submitted to PRD