Stars as Laboratories for Fundamental Physics - MPP Theory Group

522 Chapter 13
As the r.h. neutrinos escape from the inner core with much larger energies
than those from the neutrino sphere one would expect high-energy
events in the Kamiokande and IMB detectors, contrary to the observations.
Therefore, one probably needs to require µ < ν ∼ 10 −12 µ B for the
diagonal dipole moments; spin-flavor oscillations could be suppressed
by the neutrino mass differences. As the spin precession is the same for
all neutrino energies, this limit would not apply if the Earth happened
to be in a node of the oscillation pattern between SN 1987A and us.
Neutrino magnetic moments of order 10 −12 µ B could also affect the
infall phase of SNe. The spin-flip scattering on nuclei would be coherently
enhanced relative to protons. Therefore, neutrinos could escape
in the r.h. channel for much longer so that effectively trapping would
set in much later than in the standard picture (Nötzold 1988).
In and near the SN core there probably exist strong magnetic fields
of order 10 12 Gauss or more which would induce spin-precessions between
r.h. and l.h. neutrinos. Therefore, the sterile states produced in
the deep interior by spin-flip scattering could back-convert into active
ones near the neutrino sphere. Depending on details of the matterinduced
neutrino energy shifts, the vacuum mass differences, and the
magnetic field strengths and configurations this conversion could take
place inside or outside of the neutrino sphere. The observable neutrino
signal could be affected, but also the energy transfer within the SN core
and outside of the neutrino sphere. Perhaps, a more efficient transfer of
energy to the stalled shock wave could help to explode SNe in the delayed
explosion scenario. Various aspects of these scenarios have been
studied by Dar (1987), Nussinov and Rephaeli (1987), Goldman et al.
(1988), Voloshin (1988), Okun (1988), Blinnikov and Okun (1988), and
Athar, Peltoniemi, and Smirnov (1995).
Clearly, Dirac magnetic or transition moments in the 10 −12 µ B range
and below would affect SN dynamics and the observable neutrino signal
in interesting ways. However, because there are so many parameters
and possible field configurations, it is hard to develop a clear view of
the excluded or desired neutrino properties. If compelling evidence for
nonstandard neutrino electromagnetic properties in this range were to
emerge, SN dynamics likely would have to be rethought from scratch.
13.8.4 Millicharges
Within the particle physics standard model it is not entirely impossible
that neutrinos have small electric charges (Sect. 15.8). In this
case neutrinos would have to be Dirac fermions and so the r.h. states