Cosmic neutrinos of ultra-high energies and detection possibility

Abstract

The fluxes and spectra of galactic and extragalactic neutrinos at energy 10¹¹–10¹⁹ eV are calculated. In particular, the neutrino flux from the normal galaxies is calculated taking into account the spectral index distribution. The only assumption that seriously affects the calculated neutrino flux atE _v ≳10¹⁷ eV is the power-like generation spectrum of protons in the entire considered energy region.

The normal galaxies with the accepted parameters generate the metagalactic equivalent electron component (electrons+their radiation) with energy densityω _e≈8.5×10⁻⁷ eV cm⁻³, while the density of the observed diffuse X-ray radiation alone is 100 times higher. This requires the existence of other neutrino sources and we found the minimized neutrino flux under two limitations: (1) the power-law generation spectrum of protons and (2) production of the observed energy density of the diffuse X-an γ-radiation. These requirements are met in the evolutionary model of origin of the metagalactic cosmic rays with modern energy densityω _M8≈3.6×10⁻⁷ eV cm⁻³.

The possibility of experiments with cosmic neutrinos of energyE _v ≳3×10¹⁷ eV is discussed. The upper bound on neutrino-nucleon cross-section σ<2.2×10⁻²⁹ cm² is obtained in evolutionary model from the observed zenith angular distribution of extensive air showers.

In Appendix 2 the diffuse X-and γ-ray flux arising together with neutrino flux is calculated. It agrees with observed flux in the entire energy range from 1 keV up to 100 MeV.