Stars as Laboratories for Fundamental Physics - MPP Theory Group

What Have We Learned from SN 1987A 519
neutrino signal is not affected as significantly as one might have expected.
The Dirac mass limit becomes only slightly more restrictive if
mixing is assumed (Burrows, Gandhi, and Turner 1992).
Neutrinos with masses in the keV range must decay sufficiently fast
in order to avoid “overclosing” the universe. If r.h. Dirac-mass neutrinos
escape directly from the inner core of a SN they have energies
far in excess of l.h. neutrinos emitted from the neutrino sphere. If
their decay products involve sequential l.h. neutrinos or antineutrinos,
these daughter states would have caused high-energy events at IMB or
Kamiokande II, contrary to the observations. Dodelson, Frieman, and
Turner (1992) found that this argument excludes the lifetime range
10 −9 s/keV ∼ < τ/m ν ∼ < 5×10 7 s/keV, (13.16)
for Dirac masses in the range 1 keV ∼ < m ν ∼ < 300 keV, assuming that
the “visible” channel dominates.
13.8.2 Right-Handed Currents
On some level r.h. weak gauge interactions may exist as, e.g. in leftright
symmetric models where the gauge bosons which couple to r.h.
currents would differ from the standard ones only in their mass. In the
low-energy limit relevant for processes in stars one may account for the
novel couplings by a “r.h. Fermi constant” which is given as ϵG F with ϵ
some small dimensionless number which may be different for chargedand
neutral-current processes. In left-right symmetric models one finds
explicitly for charged-current reactions (Barbieri and Mohapatra 1989)
ϵ 2 CC = ζ 2 + (m WL /m WR ) 4 , (13.17)
where m WR,L are the r.h. and l.h. charged gauge boson masses while ζ
is the left-right mixing parameter.
In order to constrain ϵ CC one assumes the existence of r.h. ν e ’s so
that the dominant energy-loss mechanism of a SN core is e + p →
n + ν e,R where the final-state r.h. neutrino escapes freely. Initially, a
substantial fraction of the thermal energy of a SN core is stored in
the degenerate electron sea. Therefore, the time scale of cooling is
estimated by the inverse scattering rate for e + p → n + ν e,R . The usual
charged-current weak scattering cross section involving nonrelativistic
nucleons is G 2 F(CV 2 +3CA)E 2 e 2 /π with CV 2 +3CA 2 ≈ 4 in a nuclear medium
(Appendix B). Using a proton density corresponding to nuclear matter
at 10 15 g cm −3 and using 100 MeV for a typical electron energy one finds