1111.6690 (Brian Feldstein et al.)

Large Mixing Angles From Many Right-Handed Neutrinos    [PDF]

Brian Feldstein, William Klemm

A beautiful understanding of the smallness of the neutrino masses may be
obtained via the seesaw mechanism, whereby one takes advantage of the key
qualitative distinction between the neutrinos and the other fermions:
right-handed neutrinos are gauge singlets, and may therefore have large
Majorana masses. The standard seesaw mechanism, however, does not address the
apparent lack of hierarchy in the neutrino masses compared to the quarks and
charged leptons, nor the large leptonic mixing angles compared to the small
angles of the CKM matrix. In this paper, we will show that the singlet nature
of the right-handed neutrinos may be taken advantage of in one further way in
order to solve these remaining problems: Unlike particles with gauge
interactions, whose numbers are constrained by anomaly cancellation, the number
of gauge singlet particles is essentially undetermined. If large numbers of
gauge singlet fermions are present at high energies - as is suggested, for
example, by various string constructions - then the effective low energy
neutrino mass matrix may be determined as a sum over many distinct Yukawa
couplings, with the largest ones being the most important. This can reduce
hierarchy, and lead to large mixing angles. Assuming a statistical distribution
of fundamental parameters, we will show that this scenario leads to a good fit
to low energy phenomenology, with only a few qualitative assumptions guided by
the known quark and lepton masses. The scenario leads to predictions of a
normal hierarchy for the neutrino masses, and a value for the |m_ee| mass
matrix element of about 1-6 meV.

View original: http://arxiv.org/abs/1111.6690