EFFECTS OF NEUTRINO OSCILLATION ON THE SUPERNOVA RELIC NEUTRINO BACKGROUND

We investigate to what extent the oscillation or conversion of neutrin os enhances the expected event rate of the supernova relic neutrino ba ckground (SRN) at the Super-Kamiokande detector (SK). The SRN <(nu)ove r bar (e)>'s can be almost completely exchanged with nu(mu)-like neutr inos by the MSW oscillation under the inverse mass hierarchy with Delt a m(2) similar to 10(-8)-10(5)[eV(2)], or by the magnetic moment of Ma jorana neutrinos with mu(n)u greater than or similar to 10(-12)mu(B) a nd Delta m(2) similar to 10(-4)-10(0) [eV(2)]. In the standard calcula tion of the SRN flux, the event rate of the SRN <(nu)over bar (e)>'s a t the SK in the observable energy range of 15-40 MeV can be enhanced f rom 1.2 yr(-1) to 2.4 yr(-1) if all <(nu)over bar (e)>'s are exchanged with nu(mu)-like neutrinos. The enhancement is prominent especially i n the high energy range (greater than or similar to 25 MeV). In the as trophysically optimistic calculation, the event rate becomes as high a s 9.4 yr(-1). Because the theoretical upper bound of the SRN events wi thout oscillation is about 5 yr(-1) taking into account the various as trophysical uncertainties, we might have to resort to the neutrino osc illation if more than 5 events in a year, as well as a significantly h arder spectrum, were observed in the SK.