Neutrino oscillations in the early Universe

We discuss the oscillations effects on neutrinos in the early Universe and update the cosmological constraints on the oscillation parameters. It is shown that sterile LOW solution to the solar neutrino problem is almost completely excluded from cosmological nucleosynthesis considerations. Two possibilities for the relaxation of this constraint are discussed: high primordial helium-4 yield and a relic lepton asymmetry present at nucleosynthesis epoch. The numerical analysis proved that Y_p=0.25 only relaxes the constraint on LOW solution, while L > 10^{-5} is capable to remove it.Comment: 4 pages, 3 eps figures included, espcrc2.sty, talk at NOW2000 Workshop, 11-16 September 2000, Otranto, Italy, to be published in Nucl. Phys. B Supp

BBN with Late Electron-Sterile Neutrino Oscillations - The Finest Leptometer

A relic lepton asymmetry orders of magnitude bigger than the baryon one may hide in the relic neutrino background. No direct theoretical or experimental limitations on its magnitude and sign are known. Indirect cosmological constraints exist ranging from $|L|<0.01$ to $L<10$. We discuss a BBN model with late electron-sterile neutrino oscillations which is a fine leptometer - it is capable of feeling extremely small relic lepton asymmetry - $|L|>10^{-8}$. This sensitivity is achieved through the influence of such small $L$ on the neutrino oscillations, suppressing or enhancing them, and thus changing the primordially produced $^4He$. The influence of $L$ on nucleons freezing in pre-BBN epoch is numerically analyzed in the full range of the oscillation parameters of the model and for $L \ge 10^{-10}$. The case of oscillations generated asymmetry by late electron-sterile oscillations and its effect on primordial $^4He$ is also briefly discussed.Comment: 13 pages, 6 fig

Overproduction of primordial helium-4 in the presence of neutrino oscillations

The maximum overproduction of helium-4 in cosmological nucleosynthesis with active--sterile neutrino oscillations, nu_e -> nu_s, efficient after decoupling of electron neutrino, is analyzed. The kinetic effects on primordial nucleosynthesis due to neutrino spectrum distortion, caused by oscillations, are precisely taken into account. The maximum overproduction of primordial He-4 as a function of oscillation parameters is obtained from the analysis of the kinetics of the nucleons and the oscillating neutrinos, for the full range of parameters of the discussed oscillation model. A maximum relative increase of He-4, up to 14% for non-resonant oscillations and up to 32% for resonant ones is registered. Cosmological constraints on oscillation parameters are also discussed.Comment: 17 pages, 5 figures, much extended version, references and 3 figures adde

Vast Antimatter Regions and Scalar Condensate Baryogenesis

The possibility of natural and abundant creation of antimatter in the Universe in a SUSY-baryogenesis model with a scalar field condensate is described. This scenario predicts vast quantities of antimatter, corresponding to galaxy and galaxy cluster scales today, separated from the matter ones by baryonically empty voids. Theoretical and observational constraints on such antimatter regions are discussed.Comment: 7 pages, 2 figures, paper presented at 14th Rencontres de Blois: Matter - Antimatter Asymmetry, Chateau de Blois, France, 17-22 Jun 2002, to be published in the proceedings, ed. J. Tran Thanh Va

BARYOGENESIS MODEL SUGGESTING ANTIGALAXIES

Abstract A non-GUT baryogenesis model, according to which our Universe may contain clusters of antigalaxies is discussed. A mechanism of separation of vast quantities of matter from such of antimatter is described. The provided analysis showed that for a natural range of model parameters a sufficient separation between matter and antimatter regions, required from observational data, can be obtained