Stars as Laboratories for Fundamental Physics - MPP Theory Group

What Have We Learned from SN 1987A 513
13.6 How Many Neutrino Flavors
One may ask how the neutrino signal from a SN would be modified
if there existed additional light sequential neutrino flavors beyond ν e ,
ν µ , and ν τ . Of course, the Z ◦ decay width measured at CERN already
reveals that there are exactly three sequential neutrino flavors (Particle
Data Group 1994); the same conclusion is reached from studies of big
bang nucleosynthesis (e.g. Kolb and Turner 1990).
Burrows, Ressell, and Turner (1990) calculated several protoneutron
star cooling sequences, varying the number of flavors from 3, the
standard value, to 11. This increases the efficiency of energy transfer
within the SN core and also allows for a more efficient radiation from
the neutrino sphere as there are more degrees of freedom. Thus one
expects a shortened signal in the Kamiokande II and IMB detectors,
as well as a reduced number of events because the available energy is
shared between more neutrino degrees of freedom of which mostly the
Fig. 13.6. Number of events N KII and N IMB in the Kamiokande and IMB
detectors as well as the signal duration t KII and t IMB (in sec) as a function
of the assumed number of neutrino flavors (Burrows, Ressell, and Turner
1990). The signal duration is defined as the time it takes to accrue 90% of
the total expected number of events.