Viability of bi-maximal solution of the Zee mass matrix

We know $L_e-L_\mu-L_\tau$ symmetry gives $m^2_1= m^2_2 >> m^2_3$ pattern in Zee model. $\Delta m^2_\odot$ emerges from a small breaking of this symmetry. Because this symmetry is broken very weakly $\theta_\odot$ does not deviate much from $\tan^2 \theta_\odot=1$ which is its value in the symmetric limit. This gives a mismatch with LMA solution where mixing is large but not exactly maximal. We confront this property of Zee mass matrix by phenomenologically analyzing recent results from solar and atmospheric neutrino oscillation experiments at various confidence levels. We conclude that LOW type solution is compatible with the Zee mass matrix at 99% confidence level when atmospheric neutrino deficit is explained by maximal $\nu_\mu \leftrightarrow \nu_\tau$ oscillation. Thus the minimal version of the Zee model even though disfavored by the LMA type or VO type solutions, is compatible with LOW type solution of solar neutrino problem.Comment: This version is accepted in Physics Letters

Experimental limits on the proton life-time from the neutrino experiments with heavy water

Experimental data on the number of neutrons born in the heavy water targets of the large neutrino detectors are used to set the limit on the proton life-time independently on decay mode through the reaction d -> n+?. The best up-to-date limit tau_p > 4 10^23 yr with 95% C.L. is derived from the measurements with D_2O target (mass 267 kg) installed near the Bugey reactor. This value can be improved by six orders of magnitude with future data accumulated with the SNO detector containing 1000 t of D_2O.Comment: LaTeX, 7 pages, 1 table; small typo is correcte

Reactor as a Source of Antineutrinos: Thermal Fission Energy

Deeper insight into the features of a reactor as a source of antineutrinos is required for making further advances in studying the fundamental properties of the neutrino. The relationship between the thermal power of a reactor and the rate of the chain fission reaction in its core is analyzed.Comment: 15 pages in LaTex and 4 ps figure

Probing the matter term at long baseline experiments

We consider (\nu_\mu --> \nu_e) oscillations in long baseline experiments within a three flavor framework. A non-zero measurement of this oscillation probability implies that the (13) mixing angle `phi' is non-zero. We consider the effect of neutrino propagation through the matter of earth's crust and show that, given the constraints from solar neutrino and CHOOZ data, matter effects enhance the mixing for neutrinos rather than for anti-neutrinos. We need data from two different experiments with different baseline lengths (such as K2K and MINOS) to distinguish matter effects unambiguously.Comment: 9 pages including three figure

Testing whether muon neutrino flavor mixing is maximal

The small difference between the survival probabilities of muon neutrino and antineutrino beams, traveling through earth matter in a long baseline experiment such as MINOS, is shown to be an important measure of any possible deviation from maximality in the flavor mixing of those states.Comment: Some revision has been made in the experimental discussions with two new figures replacing the old ones and a clarification of the accuracy of the perturbative result has been included. This version will be published in Physical Review Letters. Title changed as asked by the editors of Physical Review Letter

Constraints on mixing angles of Majorana neutrinos

By combining the inputs from the neutrinoless double beta decay and the fits of cosmological models of dark matter with solar and atmospheric neutrino data, we obtain constraints on two of the mixing angles of Majorana neutrinos, which become stronger when coupled with the reactor neutrino data. These constraints are strong enough to rule out Majorana neutrinos if the small angle solution of solar neutrino puzzle is borne out.Comment: Some corrections and clarifications adde

Three Generation Neutrino Oscillation Parameters after SNO

We examine the solar neutrino problem in the context of the realistic three neutrino mixing scenario including the SNO charged current (CC) rate. The two independent mass squared differences $\Delta m^2_{21}$ and $\Delta m^2_{31} \approx \Delta m^2_{32}$ are taken to be in the solar and atmospheric ranges respectively. We incorporate the constraints on $\Delta$m$^2_{31}$ as obtained by the SuperKamiokande atmospheric neutrino data and determine the allowed values of $\Delta m^2_{21}$, $\theta_{12}$ and $\theta_{13}$ from a combined analysis of solar and CHOOZ data. Our aim is to probe the changes in the values of the mass and mixing parameters with the inclusion of the SNO data as well as the changes in the two-generation parameter region obtained from the solar neutrino analysis with the inclusion of the third generation. We find that the inclusion of the SNO CC rate in the combined solar + CHOOZ analysis puts a more restrictive bound on $\theta_{13}$. Since the allowed values of $\theta_{13}$ are constrained to very small values by the CHOOZ experiment there is no qualitative change over the two generation allowed regions in the $\Delta m^2_{21} - \tan^2 \theta_{12}$ plane. The best-fit comes in the LMA region and no allowed area is obtained in the SMA region at 3$\sigma$ level from combined solar and CHOOZ analysis.Comment: One reference added. Version to apprear in PR

Impact of CP phases on neutrinoless double beta decay

We highlight in a model independent way the dependence of the effective Majorana mass parameter, relevant for neutrinoless double beta decay, on the CP phases of the PMNS matrix, using the most recent neutrino data including the cosmological WMAP measurement. We perform our analysis with three active neutrino flavours in the context of three kinds of mass spectra: quasi-degenerate, normal hierarchical and inverted hierarchical. If a neutrinoless double beta decay experiment records a positive signal, then assuming that Majorana masses of light neutrinos are responsible for it, we show how it might be possible to discriminate between the three kinds of spectra.Comment: 10 pages, latex, 9 eps figs, version to appear in Phys Rev

Lepton number violating interactions and their effects on neutrino oscillation experiments

Mixing between bosons that transform differently under the standard model gauge group, but identically under its unbroken subgroup, can induce interactions that violate the total lepton number. We discuss four-fermion operators that mediate lepton number violating neutrino interactions both in a model-independent framework and within supersymmetry (SUSY) without R-parity. The effective couplings of such operators are constrained by: i) the upper bounds on the relevant elementary couplings between the bosons and the fermions, ii) by the limit on universality violation in pion decays, iii) by the data on neutrinoless double beta decay and, iv) by loop-induced neutrino masses. We find that the present bounds imply that lepton number violating neutrino interactions are not relevant for the solar and atmospheric neutrino problems. Within SUSY without R-parity also the LSND anomaly cannot be explained by such interactions, but one cannot rule out an effect model-independently. Possible consequences for future terrestrial neutrino oscillation experiments and for neutrinos from a supernova are discussed.Comment: 28 pages, 2 figures, Late