Stars as Laboratories for Fundamental Physics - MPP Theory Group

Nonstandard Neutrinos 279
where m ν is the mass of the decaying parent neutrino. Of these limits,
all except the cosmic one are based on measured neutrino fluxes. For
nonelectron neutrinos, the cosmic and SN 1987A limits apply equally
because these sources emit neutrinos of all flavors.
The SN 1987A constraints apply in this form only for m < ν ∼ 40 eV,
and for total lifetimes which in the laboratory exceed the transit time
between the SN and Earth. The cosmological limit assumes that the radiative
channel dominates and as such it requires m < ν ∼ 30 eV; otherwise
the universe would be “overclosed” by neutrinos. Because m < νe ∼ 5 eV
these conditions are plausibly satisfied for ν e . For ν µ and ν τ one may
contemplate masses in excess of 30 eV if one simultaneously contemplates
novel interactions which allow for invisible fast decays. Therefore,
radiative decay limits for ν µ and ν τ must be derived as a function
of the assumed mass and of the assumed total decay time. For
SN 1987A this exercise will be performed in Sect. 12.4.5, the results
are displayed in Fig. 12.17. For cosmic neutrinos, I do not know of a
published comparable contour plot.
7.5.5 Plasmon Decay in Stars
The last and most interesting constraint arises from the energy-loss
argument applied to globular cluster stars. The neutrino emissivity by
the plasma process γ → νν would be too large unless
µ ν ∼ < 3×10 −12 µ B . (7.33)
This bound, which applies for m ν ∼ < 5 keV, has been derived in detail
in Sect. 6.5.6.