arXiv subjects

P. Di Bari

Publications and source records attributed to P. Di Bari.

23 records · Page 2Linked to original sources

arXiv2000

Comment on ``Neutrino oscillations in the early universe: how can large lepton asymmetry be generated?"

We comment on the recent paper by A. D. Dolgov, S. H. Hansen, S. Pastor and D. V. Semikoz (DHPS) [Astropart. Phys. {\bf 14}, 79 (2000)] on the generation of neutrino asymmetries from active-sterile neutrino oscillations. We demonstrate that the approximate asymmetry evolution equation obtained therein is an expansion, up to a minor discrepancy, of the well-established static approximation equation, valid only when the supposedly new higher order correction term is small. In the regime where this so-called ``back-reaction'' term is large and artificially terminates the asymmetry growth, their evolution equation ceases to be a faithful approximation to the Quantum Kinetic Equations (QKEs) simply because pure Mikheyev-Smirnov-Wolfenstein (MSW) transitions have been neglected. At low temperatures the MSW effect is the dominant asymmetry amplifier. Neither the static nor the DHPS approach contains this important physics. Therefore we conclude that the DHPS results have sufficient veracity at the onset of explosive asymmetry generation, but are invalid in the ensuing low temperature epoch where MSW conversions are able to enhance the asymmetry to values of order $0.2 - 0.37$. DHPS do claim to find a significant final asymmetry for very large $δm^2$ values. However, for this regime the effective potential they employed is not valid.

hep-ph↗

arXiv2000

Active-sterile neutrino oscillations in the early Universe and the atmospheric neutrino anomaly

Cosmology cannot rule out the solution nu_mu <-> nu_s to the atmospheric neutrino data and thus only Earth experiments will be able to give a definitive answer. This conclusion holds when a generation of lepton number is taken into account and one assumes that the sterile neutrino is also slightly mixed with an eV-tau neutrino. This result cannot be spoiled by a chaotic generation of lepton domains.

hep-ph↗

arXiv2000

On the sign of the neutrino asymmetry induced by active-sterile neutrino oscillations in the early Universe

We deal with the problem of the final sign of the neutrino asymmetry generated by active-sterile neutrino oscillations in the Early Universe solving the full momentum dependent quantum kinetic equations. We study the parameter region $10^{-2} \stackrel{<}{\sim} |δm^2|/eV^2\le 10^3$. For a large range of $\sin^2 2θ_0$ values the sign of the neutrino asymmetry is fixed and does not oscillate. For values of mixing parameters in the region $10^{-6}\stackrel{<}{\sim}\sin^{2}2θ_{0}\stackrel{<}{\sim} 3\times 10^{-4} ({\rm eV}^{2}/|δm^{2}|)$, the neutrino asymmetry appears to undergo rapid oscillations during the period where the exponential growth occurs. Our numerical results indicate that the oscillations are able to change the neutrino asymmetry sign. The sensitivity of the solutions and in particular of the final sign of lepton number to small changes in the initial conditions depends whether the number of oscillations is high enough. It is however not possible to conclude whether this effect is induced by the presence of a numerical error or is an intrinsic feature. As the amplitude of the statistical fluctuations is much lower than the numerical error, our numerical analysis cannot demonstrate the possibility of a chaotical generation of lepton domains. In any case this possibility is confined to a special region in the space of mixing parameters and it cannot spoil the compatibility of the $ν_μ\leftrightarrowν_{s}$ solution to the neutrino atmospheric data obtained assuming a small mixing of the $ν_{s}$ with an ${\rm eV}-τ$ neutrino.

hep-ph↗

arXiv1999

Amplification of Isocurvature Perturbations induced by Active-Sterile Neutrino Oscillations

We show how the generation of a lepton number in the Early Universe induced by active-sterile neutrino oscillations, in presence of small baryon number inhomogeneities, gives rise to the formation of lepton domains, regions with different values of active neutrino chemical potential. The structure of these domains reflects the spectral features of the baryon number inhomogeneities that generated it. An interesting aspect of the mechanism is that the size of lepton domains can be super-horizon.

hep-ph↗

arXiv1997

Entropy production in the Early Universe. A new mechanism

We expose briefly the role of entropy in the early universe and in particular the importance of searching for new mechanisms of entropy production. We describe a mechanism that shows how entropy is produced during early annihilations and under which conditions the production is not negligible. A MeV tau neutrino provides an interesting application.

hep-ph↗