53 research outputs found

    Seesaw mechanism and the neutrino mass matrix

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    The seesaw mechanism of neutrino mass generation is analysed under the following assumptions: (1) minimal seesaw with no Higgs triplets, (2) hierarchical Dirac masses of neutrinos, (3) large lepton mixing primarily or solely due to the mixing in the right-handed neutrino sector, and (4) unrelated Dirac and Majorana sectors of neutrino masses. It is shown that large mixing governing the dominant channel of the atmospheric neutrino oscillations can be naturally obtained and that this constrained seesaw mechanism favours the normal mass hierarchy for the light neutrinos leading to a small Ue3U_{e3} entry of the lepton mixing matrix and a mass scale of the lightest right handed neutrino M10101011M\simeq 10^{10} - 10^{11} GeV. Any of the three main neutrino oscillation solutions to the solar neutrino problem can be accommodated. The inverted mass hierarchy and quasi-degeneracy of neutrinos are disfavoured in our scheme.Comment: LaTeX, 3 pages, no figures. Talk given at 6th International Workshop on Topics in Astroparticle and Underground Physics (TAUP 99), September 6-10, 1999, Paris, Franc

    Small entries of neutrino mass matrices

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    We consider phenomenologically allowed structures of the neutrino mass matrix in the case of three light neutrino species. Constraints from the solar, atmospheric and reactor neutrino experiments as well as those from the neutrinoless double beta decay are taken into account. Both hierarchical and quasi-degenerate neutrino mass cases are studied. Assuming maximal νμντ\nu_\mu-\nu_\tau mixing we derive simple approximate expressions giving the values of the neutrino masses and remaining lepton mixing angles in terms of the entries of the neutrino mass matrix. Special attention is paid to the small entries which are usually not specified in discussions of the neutrino mass matrix textures. We specifically discuss the stability of neutrino masses and lepton mixing angles with respect to the choice and variations of these small entries.Comment: LaTeX, 12 pages, no figures. A few minor typos correcte

    Neutrino oscillograms of the Earth and CP violation in neutrino oscillations

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    An analysis of 3-flavour neutrino oscillations inside the Earth is presented in terms of the oscillograms -- contour plots of oscillation probabilities in the plane neutrino energy -- nadir angle. Special attention is paid to CP violation in neutrino oscillations in the Earth.Comment: Talk given at Neutrino Oscillations Workshop NOW2008, 3 pages, 2 figure

    Neutrinos with Mixing in Twisting Magnetic Fields

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    Transitions in a system of neutrinos with vacuum mixing and magnetic moments, propagating in matter and transverse magnetic field, are considered. It is shown that in the realistic case of magnetic field direction varying along the neutrino path qualitatively new phenomena become possible: permutation of neutrino conversion resonances, appearance of resonances in the neutrino-antineutrino (νlLνˉlR\nu_{lL}\leftrightarrow\bar{\nu}_{lR}) transition channels, neutrino-antineutrino resonant conversion, large amplitude νlLνˉlR\nu_{lL}\leftrightarrow\bar{\nu}_{lR} oscillations, merging of different resonances (triple resonances). Possible phenomenological implications of these effects are briefly discussed.Comment: LaTeX, 35 pages, 4 figures (not included but available upon request). In memoriam of Ya.A. Smorodinsky. SISSA-170/92/E

    Pontecorvo's Original Oscillations Revisited

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    We show that a left-handed neutrino νL\nu_L can oscillate into its CPCP- conjugated state νˉR\bar{\nu}_R with maximal amplitude, in direct analogy with K0Kˉ0K^0-\bar{K}^0 oscillations. Peculiarities of such oscillations under different conditions are studied.Comment: LaTeX, 14 pages, 1 figure (not included but available upon request by fax or ordinary mail), SISSA 9/93/EP, IC/93/1

    Matter effects in oscillations of neutrinos traveling short distances in matter

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    It is well known that when the distance tt traveled by neutrinos in matter is short, matter effects in oscillations of neutrino flavour are small and decrease with decreasing tt more rapidly than the oscillations effects themselves. We discuss the reason for this and demonstrate that under certain circumstances this statement is no longer correct. In particular, we show that if neutrinos propagate significant distances in vacuum before entering matter (or after exiting it), matter effects in short-tt neutrino oscillations can be significantly enhanced. Implications for oscillations of solar and atmospheric neutrinos with nearly horizontal trajectories inside the earth and for accelerator experiments are considered. We also comment on neutrino oscillations in matter due to flavour changing neutral currents.Comment: LaTeX, 10 pages. Title changed, references added, minor textual changes. Final version to be published in Phys. Lett.

    Implications of Gallium Solar Neutrino Data for the Resonant Spin-Flavor Precession Scenario

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    We consider the implications of the recent results of SAGE and GALLEX experiments for the solution of the solar neutrino problem in the framework of the resonant neutrino spin-flavor precession scenario. It is shown that this scenario is consistent with all the existing solar neutrino data including the gallium results. The quality of the fit of the data depends crucially on the magnetic field profile used which makes it possible to get information about the magnetic field in the solar interior. In particular, the magnetic field in the core of the sun must not be too strong (<3×106<3 \times 10^6 G). The detection rate in the gallium detectors turns out to be especially sensitive to the magnitude of Δm2\Delta m^2. Predictions for forthcoming solar-neutrino experiments are made.Comment: LaTeX, 16 pages, 5 figures (not included by available upon request by fax or ordinary mail
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