The duration of the neutrino burst observed by Kamiokande II and IMB h
as been used to deduce upper bounds on novel long-range forces couplin
g supernova neutrinos and electrons in our galaxy. Consequences of pos
sible existence of such forces, mediated by leptonic photons, on matte
r-enhanced neutrino flavor transformation in the core of the nascent n
eutron star and its surrounding mantle, are analyzed.