Stars as Laboratories for Fundamental Physics - MPP Theory Group

Neutrinos: The Bottom Line 573
Apart from the detector signal, the oscillation of SN neutrinos can
have important implications for SN physics itself because of the swap
of, say, the ν e with the ν τ spectrum which is much harder. For a mass
difference corresponding to the cosmologically interesting range of a few
to a few tens of eV, resonant oscillations could occur so close to the neutrino
sphere that the “crossover” point is within the stalling shock wave
in the delayed-explosion scenario. The effective hardening of the ν e
spectrum would then enhance the neutrino energy transfer to the shock
wave, thus helping to explode supernovae (Sect. 11.4.4). Conversely, a
few seconds after collapse the same effect would drive the hot wind
proton rich which is driven from the surface of the compact remnant.
This effect would prevent the occurrence of r-process nucleosynthesis
which requires a neutron-rich environment (Sect. 11.4.5). Interestingly,
because the remnant is more compact at “late” times (few seconds after
collapse), the adiabaticity condition can be met only for relatively large
mixing angles. Thus, there is a plausible range of neutrino parameters
where oscillations may help to explode supernovae, and still r-process
nucleosynthesis may proceed undisturbed (Fig. 11.20). At any rate, it
is impossible to ignore neutrino oscillations for SN physics if neutrino
masses happen to lie in the cosmologically interesting range.
16.2.4 Electromagnetic Properties
In the Minimally Extended Standard Model neutrinos have magnetic
and electric diagonal and transition moments which are proportional to
their assumed masses (Sect. 7.2.2). Because of the cosmological mass
limit these quantities are so small that they do not seem to be important
anywhere. However, one may toy with the idea that neutrinos actually
carry small electric charges, a possibility that is not entirely excluded
by the structure of the Standard Model if one gives up the notion that
the second and third particle families are exact replicas of the first
except for the masses (Sect. 15.8).
The possible magnitude of a ν e charge is limited by e νe ∼ < 3×10 −17 e
from the absence of an anomalous dispersion of the SN 1987A neutrino
burst (Sect. 13.3.3). All neutrino charges are limited by e ν ∼ <
2×10 −14 e from the absence of anomalous cooling of globular-cluster
stars (Sect. 6.5.6). For ν µ and ν τ the cosmological mass limit is crucial
for this bound because their emission would be suppressed by threshold
effects if their mass exceeded the relevant plasma frequency of a few
keV. The assumption of charge conservation in β decay yields a more
restrictive limit e νe ∼ < 3×10 −21 (Sect. 15.8).