COSMIC NEUTRINO RADIATION IN THE FAR ULTRAVIOLET AND THE E6 MODEL

Observations of the cosmic ultraviolet background by the Berkeley UVX spectrometer sets an upper limit to the intensity of radiation due to possibly existing radiatively decaying primordial particles in the mass range 13.5-17.5 eV. If such particles exist with a number density equalling that of neutrinos today they must have a lifetime exceeding 4.6 x 10(23) s. We explore the idea of Sciama that tau neutrinos nu-tau of mass 29 +/- 1 eV with a lifetime of (2 +/- 1) x 10(23) s decay raditively into nu-mu or nu-e, thereby being responsible for the ionization of interstellar and intergalactic hydrogen (the Gunn-Petersen effect). In the standard model this is impossible, however, in the context of an E6 model the neutrinos may have radiative lifetimes of the order of 10(23) s.