Summary: Stringent constraints on cosmological neutrino­antineutrino asymmetries
from synchronized flavor transformation
Kevork N. Abazajian, John F. Beacom, and Nicole F. Bell
NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510­0500
aba@fnal.gov, beacom@fnal.gov, nfb@fnal.gov
(Dated: March 25th, 2002)
We assess a mechanism which can transform neutrino­antineutrino asymmetries between flavors
in the early universe, and confirm that such transformation is unavoidable in the near bi­maximal
framework emerging for the neutrino mixing matrix. We show that the process is a standard
Mikheyev­Smirnov­Wolfenstein flavor transformation dictated by a synchronization of momentum
states. We also show that flavor ``equilibration'' is a special feature of maximal mixing, and carefully
examine new constraints placed on neutrino asymmetries. In particular, the big bang nucleosyn­
thesis limit on electron neutrino degeneracy |#e | . 0.04 does not apply directly to all flavors, yet
confirmation of the large­mixing­angle solution to the solar neutrino problem will eliminate the
possibility of degenerate big bang nucleosynthesis.
PACS numbers: 14.60.Pq, 26.35.+c FERMILAB­Pub­02/056­A
I. INTRODUCTION
As is well known, the observational successes of big
bang nucleosynthesis (BBN) are one of the pillars of stan­
dard cosmology [1]. If one assumes three standard neu­

Source: Abazajian, Kev - Theoretical Astrophysics, Fermilab

Collections: Physics