Discrete Gauge Symmetries in Axionic Extensions of the SSM

We examine discrete gauge symmetries in axionic extensions of the SSM which provide a solution of the $\mu$-problem. Automatic-PQ symmetry and proton stability are shown to be guaranteed by certain discrete symmetries. Focusing on the L-violating discrete symmetries we discuss two sources of neutrino masses and their relevance for the solar neutrino problem.Comment: 13 pages, TUM-TH-150/92, MPI-Ph/92-7

Where are the beryllium neutrinos?

We show that present experiments imply that neutrinos are nonstandard at the 87\% C.L., independently of solar or nuclear physics. Moreover, if neutrinos are standard, the $^7$Be flux must be almost zero. Even if we arbitrarily disregard one of the experiments, the neutrino flux must still be less than half of the value predicted by standard solar models.Comment: 8 pages in RevTeX 3.0 plus 2 figures in uuencoded postscript files. Full postscript version available via anonymous ftp from risc0.ca.infn.it:/pub/private/lissia/infnfe-10-94.ps (192.84.132.4) Submitted to Physics Letters

An Inverted Mass Hierarchy for Hot Dark Matter and the Solar Neutrino Problem.

The cosmological model in which 20% of the dark matter is shared by two nearly equal mass neutrinos fits the structure of the universe on all scales. This has been motivated a $\nu_\mu$-$\nu_{\tau}$ oscillation explanation of the deficit of atmospheric muon neutrinos. If the observed ratio of atmospheric $nu_\mu$ to $\nu_e$ has an alternative explanation, the cosmological model can be retained if the deficit of solar neutrinos is explained by $\nu_e$-$\nu_{\tau}$ oscillation. In this case an inverted mass hierarchy is required with $m_{\nu_{\mu}}\ll m_{\nu_e} \simeq m_{\nu_\tau}\approx 2.4$ eV. We show that if there exists an $L_e- L_{\tau}$ symmetry in nature, both the near mass degeneracy of \nue\ and \nut\ as well as the consistency of the above values for neutrino masses with the negative results for neutrinoless double beta decay search experiments are easily understood. We show that this symmetry implemented in the context of a high-scale left-right symmetric theory with the see-saw mechanism can lead to a simple theoretical understanding of the desired form of the mass matrix.Comment: Tex file; no figures; 10 page

Neutrino Masses in Flipped SU(5)

We analyse the fermion masses and mixings in the flipped SU(5) model. The fermion mass matrices are evolved from the GUT scale down to $m_W$ by solving the renormalization group equations for the Yukawa couplings. The constraints imposed by the charged fermion data are then utilised to make predictions about the neutrino properties . It is found that the {\it generalized } see-saw mechanism which occurs naturally in this model can provide {\it i})a solution to the solar neutrino problem via the MSW mechanism and {\it ii})a sufficiently large $\nu _{\tau }$ mass to contribute as a hot dark matter component as indicated by the recent COBE data.Comment: (14 Pages,No figures,TEX,IOA-290/92 preprint

Solar and atmospheric neutrino oscillations with three flavours

We analyze the solar and the atmospheric neutrino problems in the context of three flavour neutrino oscillations. We assume a mass hierarchy in the vacuum mass eigenvalues $\mu_3^2 \gg \mu_2^2 \geq \mu_1^2$, but make no approximation regarding the magnitudes of the mixing angles. We find that there are small but continuous bands in the parameter space where the constraints imposed by the current measurements of $\ {}^{71} Ga$, ${}^{37} Cl$ and Kamiokande experiments are satisfied at $1 \sigma$ level. The allowed parameter space increases dramatically if the error bars are enlarged to $1.6 \sigma$. The electron neutrino survival probability has different energy dependence in different regions of the parameter space. Measurement of the recoil electron energy spectrum in detectors that use $\nu - e$ scattering may distinguish between some of the allowed regions of parameter space. Finally we use the results for the parameter space admitted by the solar neutrinos as an input for the atmospheric neutrino problem and show that there exists a substantial region of parameter space in which both problems can be solved.Comment: 25 pages plus eight figures. Uses Revtex. Postcript files for figures sent separately as a uuencoded fil

Phenomenology of Neutrino Oscillations

The phenomenology of solar, atmospheric, supernova and laboratory neutrino oscillations is described. Analytical formulae for matter effects are reviewed. The results from oscillations are confronted with neutrinoless double beta decay.Comment: 11 pages, 2 figures, latex, Plenary talk given at Workshop in High Energy Particle Physics-6, Chennai, Indi

Treating Solar Model Uncertainties: A Consistent Statistical Analysis of Solar Neutrino Models and Data

We describe how to consistently incorporate solar model uncertainties, along with experimental errors and correlations, when analyzing solar neutrino data to derive confidence limits on parameter space for proposed solutions of the solar neutrino problem. Our work resolves ambiguities and inconsistencies in the previous literature. As an application of our methods we calculate the masses and mixing angles allowed by the current data for the proposed MSW solution using both Bayesian and frequentist methods, allowing purely for solar model flux variations, to compare with previous work. We consider the effects of including metal diffusion in the solar models and also discuss implications for future experiments.Comment: 29 pages (incl figs), latex, 6 figures (appended as separate uuencoded file. To embed figures in text, uncomment 6 \epsfysize lines which appear before bibliography), CWRU-P5-94, CfPA-94-TTH-29, Fermilab-Pub-94/176-

Neutrino conversions in random magnetic fields and ν~e\tilde{\nu}_e from the Sun

The magnetic field in the convective zone of the Sun has a random small-scale component with the r.m.s. value substantially exceeding the strength of a regular large-scale field. For two Majorana neutrino flavors $\times$ two helicities in the presence of a neutrino transition magnetic moment and nonzero neutrino mixing we analyze the displacement of the allowed ($\Delta m^2- \sin^22\theta$)-parameter region reconciled for the SuperKamiokande(SK) and radiochemical (GALLEX, SAGE, Homestake) experiments in dependence on the r.m.s. magnetic field value $b$, or more precisely, on a value $\mu b$ assuming the transition magnetic moment $\mu = 10^{-11}\mu_B$. In contrast to RSFP in regular magnetic fields we find an effective production of electron antineutrinos in the Sun even for small neutrino mixing through cascade conversions $\nu_{eL}\to \nu_{\mu L}\to \tilde{\nu}_{eR}$, $\nu_{eL}\to \nu_{\mu R}\to \tilde{\nu}_{eR}$ in a random magnetic field that would be a signature of the Majorana nature of neutrino if $\tilde{\nu}_{eR}$ will be registered. Basing on the present SK bound on electron antineutrinos we have also found an excluded area in the same $\Delta m^2,~\sin^22\theta$-plane and revealed a strong sensitivity to the random magnetic field correlation length $L_0$.Comment: LaTex 36 pages including 14 PostScript figure

Unified explanation of the Solar and Atmospheric neutrino Puzzles in a minimal supersymmetric SO(10) model

It was recently suggested that in a class of supersymmetric SO(10) models with Higgs multiplets in 10, and a single $126+\bar{126}$ representations, if the $\bar{126}$ contributes both to the right handed neutrino masses as well as to the charged fermion masses, one can have a complete prediction of the neutrino masses and mixings. It turns out that if one chooses only one 10, there are no regions in the parameter space where one can have a large $\nu_{\mu}-\nu_{\tau}$ mixing angle necessary to solve the atmospheric neutrino deficit while at the same time solving the solar neutrino puzzle via the $\nu_e \leftrightarrow \nu_{\mu}$ oscillation. We show that this problem can be solved in a particular class of SO(10) models with a pair of 10 multiplets if we include the additional left-handed triplet contribution to the light neutrino mass matrix. This model cannot reproduce the mass and mixing parameters required to explain the LSND observations neither does it have have a neutrino hot dark matter.Comment: 4 pages and 4 figures; Version substantially different from the original one but same conclusion

The MSW solution to the solar neutrino problem for non-standard solar models

The difficulties for non-standard solar models (NSSM) in resolving the solar neutrino problem are discussed stressing the incompatibility of the gallium--Kamiokande data, and of the gallium--chlorine data. We conclude that NSSM's cannot explain simultaneously the results of any two of the solar neutrino data (chlorine, Kamiokande and gallium). We address further the question whether the MSW solution exists for NSSM's (e.g. models with $^8$B neutrino flux much lower than the standard one and/or central temperature $T_c$ very different from $T_c^{\text{SSM}}$). We demonstrate that the MSW solution exists and is very stable relative to changes of $S_{17}$ ($S$-factor for $p$ + $^7$Be reaction) and $T_c$. In particular, $\Delta m^2$ is almost constant while $\sin^2 2\theta$ depends on the exact values of $S_{17}$ (or $^8$B-neutrino flux) and $T_c$.Comment: 13 pages in RevTeX 3.0 plus 3 figures in uuencoded postscript files. Full postscript version available via anonymous ftp from risc0.ca.infn.it:/pub/private/lissia/lngs-94-104.ps (192.84.132.4) Submitted to Physics Letters