SPECTRUM OF THE RELIC NEUTRINO BACKGROUND FROM PAST SUPERNOVAE AND COSMOLOGICAL MODELS

It is greatly expected that the relic neutrino background from past su pernovae will be detected by Superkamiokande (SK) which is now under c onstruction. We calculate the spectrum and the event rate at SK system atically by using the results of simulations of a supernova explosion and reasonable supernova rates. We also investigate the effect of a co smological constant, Lambda, on the spectrum, since some recent cosmol ogical observations strongly suggest the existence of Lambda. We find following results. (1) The spectrum has a peak at about 3 MeV, which i s much lower than that of previous estimates (6-10 MeV). (2) The event rate at SK in the range from 10 MeV to 50 MeV, where the relic neutri nos from past supernovae are dominant, is about 25h(50)(2)(R(SN)/0.1 y r(-1))(n(G)h(50)(-3)/0.02 Mpc(-3)) events per year, where R(SN) is the supernova rate in a galaxy, n(G) is the number density of galaxies, a nd h(50) = H-0/(50 km/s Mpc), where H-0 is the Hubble constant. (3) Th e event rate is almost insensitive to Lambda. The flux increases in th e low energy side (< 10 MeV) with increasing Lambda, but decreases in the high energy side (> 10 MeV) in models in which the integrated numb er of supernovae in one galaxy is fixed.