39 research outputs found
Nearly degenerate neutrinos, Supersymmetry and radiative corrections
If neutrinos are to play a relevant cosmological role, they must be
essentially degenerate with a mass matrix of the bimaximal mixing type. We
study this scenario in the MSSM framework, finding that if neutrino masses are
produced by a see-saw mechanism, the radiative corrections give rise to mass
splittings and mixing angles that can accommodate the atmospheric and the
(large angle MSW) solar neutrino oscillations. This provides a natural origin
for the hierarchy. On the other hand,
the vacuum oscillation solution to the solar neutrino problem is always
excluded. We discuss also in the SUSY scenario other possible effects of
radiative corrections involving the new neutrino Yukawa couplings, including
implications for triviality limits on the Majorana mass, the infrared fixed
point value of the top Yukawa coupling, and gauge coupling and bottom-tau
unification.Comment: 32 pages, 12 Postscript figures, uses psfig.st
Naturalness of nearly degenerate neutrinos
If neutrinos are to play a relevant cosmological role, they must be
essentially degenerate. We study whether radiative corrections can or cannot be
responsible for the small mass splittings, in agreement with all the available
experimental data. We perform an exhaustive exploration of the bimaximal mixing
scenario, finding that (i) the vacuum oscillations solution to the solar
neutrino problem is always excluded; (ii) if the mass matrix is produced by a
see-saw mechanism, there are large regions of the parameter space consistent
with the large angle MSW solution, providing a natural origin for the hierarchy; (iii) the bimaximal structure becomes
then stable under radiative corrections. We also provide analytical expressions
for the mass splittings and mixing angles and present a particularly simple
see-saw ansatz consistent with all observations.Comment: 25 pages, LaTeX, 6 ps figures, psfig.sty. Typos, references and minor
details corrected. Additional condition for the MSW mechanism incorporated.
New viable textures adde
Limits on Neutrino Mass from Cosmic Structure Formation
We consider the effect of three species of neutrinos with nearly degenerate
mass on the cosmic structure formation in a low matter-density universe within
a hierarchical clustering scenario with a flat initial perturbation spectrum.
The matching condition for fluctuation powers at the COBE scale and at the
cluster scale leads to a strong upper limit on neutrino mass. For a flat
universe with matter density parameter Omega=0.3, we obtain m_nu<0.6eV for the
Hubble constant H_0<80km/s/Mpc. Allowing for the more generous parameter space
limited by Omega11.5Gyr, the limit is 0.9eV.Comment: 4 pages with 2 figure
Resonant neutrino spin-flavor precession and supernova shock revival
A new mechanism of supernova shock revival is proposed, which involves
resonant spin--flavor precession of neutrinos with a transition magnetic moment
in the magnetic field of the supernova. The mechanism can be operative in
supernovae for transition magnetic moments as small as provided
the neutrino mass squared difference is in the range . It is shown that this mechanism can increase the
neutrino--induced shock reheating energy by about 60\%.Comment: 16 pages, latex, 2 figures. added few reference
Neutrinos on Earth and in the Heavens
Recent data lead us to a simple and intriguing form of the neutrino mass
matrix. In particular, we find solar neutrino oscillations to be nearly maximal
(and rule out the small-angle MSW explanation of solar neutrino observations)
if relic neutrinos comprise at least one~percent of the critical mass density
of the universe.Comment: 7 pages, harvmac, minor changes and new references in revised versio