Majorana Neutrino Masses from Neutrinoless Double Beta Decay and Cosmology

When three Majorana neutrinos describe the solar and atmospheric neutrino data via oscillations, a nonzero measurement of neutrinoless double beta ($0\nu\beta\beta$) decay can determine the sum of neutrino masses $\sum m_\nu$ if the solar solution has small-angle mixing, and place a lower bound on $\sum m_\nu$ for large-angle solar mixing. If in addition a nonzero $\sum m_\nu$ is deduced from cosmology, the neutrino mass spectrum may be uniquely specified for some ranges of neutrino parameters. For $\sum m_\nu > 0.75$ eV, the small-angle solar solution is excluded by the current upper limit on neutrinoless double beta decay. In models with maximal solar mixing the $CP$ phases of the neutrinos may be strongly constrained by stringent upper bounds on $0\nu\beta\beta$ decay.Comment: 13 pages, Latex2.09, uses epsf.sty, 4 postscript figure

Seasonal and Energy Dependence of Solar Neutrino Vacuum Oscillations

We make a global vacuum neutrino oscillation analysis of solar neutrino data, including the seasonal and energy dependence of the recent Super-Kamiokande 708-day results. The best fit parameters for \nu_e oscillations to an active neutrino are \delta m^2 = 4.42\times10^{-10} eV^2, \sin^2 2\theta = 0.93. The allowed mixing angle region is consistent with bi-maximal mixing of three neutrinos. Oscillations to a sterile neutrino are disfavored. Allowing an enhanced hep neutrino flux does not significantly alter the oscillation parameters.Comment: Latex2.09, 10 pages, uses epsf.sty, 3 postscript figure

Testing the LMA solution with solar neutrinos independently of solar models

We perform a comparative study of two methods of determining the survival probabilities of low, intermediate, and high energy solar neutrinos that emphasizes the general agreement between the Large Mixing Angle (LMA) solution and extant solar neutrino data. The first analysis is oscillation parameter-independent and the second analysis involves an approximate calculation of the survival probabilities in the three energy ranges that depends only on oscillation parameters. We show that future experiments like BOREXino, CLEAN, Heron, LENS and MOON, that measure $pp$ and $^7$Be neutrinos, will facilitate a stringent test of the LMA solution independently of the Standard Solar Model (SSM), without recourse to earth-matter effects. Throughout, we describe the role of SSM assumptions on our results. If the LMA solution passes the test without needing to be modified, it may be possible to establish that $\theta_x$ is nonzero at more than $2\sigma$ assuming the SSM prediction for the $pp$ flux is correct.Comment: Final SNO salt-phase data included in analysis. Version to appear in PL

Piecing the Solar Neutrino Puzzle Together at SNO

We perform an oscillation parameter-independent analysis of solar neutrino flux measurements from which we predict the charged-current rate at SNO relative to Standard Solar Model to be $R_{SNO}^{CC}=0.35^{+0.16}_{-0.09} (0.46^{+0.13}_{-0.11})$ for oscillations to active (sterile) neutrinos. By alternately considering the $^8$B flux normalization fixed and free, we find that the flux measured by Super-Kamiokande (SK) not being a result of oscillations is strongly disfavored for oscillations to active neutrinos. SNO will determine the best-fit value of the $^8$B flux normalization $\beta$ (equal to the neutral-current rate), without recourse to neutral-current measurements, from the derived relation $\beta=R_{SNO}^{NC}=5.85 R_{SK} - 4.85 R_{SNO}^{CC}$. Using a simple parameterization of the fraction of high, intermediate, and low energy solar neutrinos starting above resonance, we reproduce the results of global analyses to good accuracy; we find that the LMA solution with a normal mass hierarchy is clearly favored. With $\beta$ free, our analysis for oscillations to active neutrinos gives $R_{SNO}^{NC}=\beta=1.34 \pm 0.34$, which corresponds to $R_{SNO}^{CC}=0.28\pm 0.07$.Comment: Version to appear in PL

How two neutrino superbeam experiments do better than one

We examine the use of two superbeam neutrino oscillation experiments with baselines \lsim 1000 km to resolve parameter degeneracies inherent in the three-neutrino analysis of such experiments. We find that with appropriate choices of neutrino energies and baselines two experiments with different baselines can provide a much better determination of the neutrino mass ordering than a single experiment alone. Two baselines are especially beneficial when the mass scale for solar neutrino oscillations $\delta m^2_{\rm sol}$ is \gsim 5\times10^{-5} eV$^2$. We also examine CP violation sensitivity and the resolution of other parameter degeneracies. We find that the combined data of superbeam experiments with baselines of 295 and 900 km can provide sensitivity to both the neutrino mass ordering and CP violation for $\sin^22\theta_{13}$ down to 0.03 for $|\delta m^2_{\rm atm}| \simeq 3\times10^{-3}$ eV$^2$. It would be highly advantageous to have a 10% determination of $|\delta m^2_{\rm atm}|$ before the beam energies and baselines are finalized, although if $|\delta m^2_{\rm atm}|$ is not that well known, the neutrino energies and baselines can be chosen to give fairly good sensitivity for a range of $|\delta m^2_{\rm atm}|$.Comment: 18 pages, 6 PS figures, added references and revised discussio

Neutrino Mass Matrices in Models with Horizontal Symmetries

We have studied the most general neutrino mass matrices in models with SU(2) and SU(3) horizontal symmetries. Without going into the details of the models it is possible to write down the effective operators, which predict the structure of the Majorana neutrino mass matrices. Unlike other extensions of the standard model, the structure is now independent of the effective Yukawa couplings and depends entirely on the Higgs which gives mass to the other fermions. In the case of SU(3) symmetries the lowest dimensional operators are forbidden requiring a low mass scale for lepton number violation.Comment: 11 pages latex file, a few references added in 2nd versio