Unstable massive tau-neutrinos and primordial nucleosynthesis

The impact of unstable Majorana tau neutrinos on primordial nucleosynthesis is considered. The mass and lifetime of nu_tau are taken in the intervals 0.1-20 MeV and 0.001-400 sec respectively. The studied decay modes are nu_tau -> nu_mu + phi and nu_tau -> nu_e + phi, where phi is a massless (or light) scalar. Integro-differential kinetic equations are solved numerically without any simplifying assumptions. Our results deviate rather strongly from earlier calculations. Depending on mass, lifetime, and decay channels of the nu_tau, the number of effective neutrino species (found from He4), in addition to the 3 standard ones, varies from -2 to +2.5. The abundances of H2 and Li7 are also calculated.Comment: 36 pages including 28 figures, minor change

Neutrino Properties from High Energy Astrophysical Neutrinos

It is shown that high energy neutrino beams from very distant sources can beutilized to learn about some properties fof neutrinos such as lifetimes and mass hierarchy etc. Furthermore, even mixing elements such as U-e3 and the CPV phase can be measured in principle. Pseudo-Dirac mass differences as small as 10^-18 eV^2 can be probed as well.Comment: 13 pages. Presented at the PASCOS'04 and Nath-Fest, august 16-22, 2004, Boston, to be published in the proceeding

Effects of sterile neutrinos on the ultrahigh-energy cosmic neutrino flux

We investigate the effect of sterile neutrinos that are nearly degenerate with active ones on the flux of ultrahigh-energy cosmic ray neutrinos at earth. This offers a way to probe neutrino oscillations in the mass-squared range (10^{-16} eV^2 < \delta m^2 < 10^{-11} eV^2) which maybe hard to detect by any other means. Taking into account the present experimental uncertainties of the active-active mixing angles and by allowing any values for the active-sterile mixing angles we find that the ratio of the electron and muon neutrino fluxes may change by -40 % to 70 % in comparison with the ratio in the absence of active-sterile mixing.Comment: 13 pages, 4 figures. Final version to be published in Phys. Lett.