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The Increase in the Primordial 4 He Yield in the Two-Doublet Four-Neutrino Mixing Scheme

Summary: The Increase in the Primordial 4 He Yield in the
Two-Doublet Four-Neutrino Mixing Scheme
Kevork Abazajian, George M. Fuller and Xiangdong Shi
Department of Physics, University of California, San Diego, La Jolla, California 92093-0319
(July 11, 2000)
We assess the e ects on Big Bang Nucleosynthesis (BBN) of lepton number generation in the
early universe resulting from the two-doublet four-neutrino mass/mixing scheme. It has been ar-
gued that this neutrino mass/mixing arrangement gives the most viable t to the existing data.
We study full 4  4 mixing matrices and show how possible symmetries in these can a ect the
BBN 4 He abundance yields. Though there is as yet no consensus on the reliability of BBN calcu-
lations with neutrino avor mixing, we show that, in the case where the sign of the lepton number
asymmetry is unpredictable, BBN considerations may pick out speci c relationships between mixing
angles. In particular, reconciling the observed light element abundances with a   * )  e oscillation
interpretation of LSND would allow unique new constraints on the neutrino mixing angles in this
PACS numbers: 14.60.Pq; 14.60.St; 26.35.+c; 95.30.-k
In this paper we revisit the long standing issue of how neutrino avor mixing in the early universe might a ect
Big Bang Nucleosynthesis (BBN). Though this is an old problem [1{5], with the advent of modern experiments (e.g.,
solar, atmospheric, and accelerator-based oscillation experiments) we can hope to begin constructing the neutrino


Source: Abazajian, Kev - Theoretical Astrophysics, Fermilab


Collections: Physics