Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2000-12-05
Phys.Rev.D64:073006,2001
Physics
High Energy Physics
High Energy Physics - Phenomenology
32 pages, RevTeX, 16 figures. Substantial changes in the treatment of conversion effects in the relic neutrino background and
Scientific paper
10.1103/PhysRevD.64.073006
We study matter effects on oscillations of high-energy neutrinos in the Universe. Substantial effect can be produced by scattering of the neutrinos from cosmological sources ($z\gta 1$) on the relic neutrino background, provided that the latter has large CP-asymmetry: $\eta\equiv (n_\nu-n_{\bar{\nu}})/n_\gamma\gta 1$, where $n_\nu$, $n_{\bar{\nu}}$ and $n_\gamma$ are the concentrations of neutrinos, antineutrinos and photons. We consider in details the dynamics of conversion in the expanding neutrino background. Applications are given to the diffuse fluxes of neutrinos from GRBs, AGN, and the decay of super-heavy relics. We find that the vacuum oscillation probability can be modified by $\sim (10-20)%$ and in extreme cases allowed by present bounds on $\eta$ the effect can reach $\sim 100%$. Signatures of matter effects would consist (i) for both active-active and active-sterile conversion, in a deviation of the numbers of events produced in a detector by neutrinos of different flavours, $N_{\alpha}~(\alpha=e,\mu,\tau)$, and of their ratios from the values given by vacuum oscillations; such deviations can reach $\sim 5-15%$, (ii) for active-sterile conversion, in a characteristic energy dependence of the ratios $N_{e}/N_{\mu},N_{e}/N_{\tau},N_{\mu}/N_{\tau}$. Searches for these matter effects will probe large CP and lepton asymmetries in the universe.
Lunardini Cecilia
Smirnov Alexei Yu.
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