On universality of the coupling of neutrinos to Z

We employ an effective Lagrangian approach and use LEP data to place severe bounds on universality violations of the couplings of $\nu_e$, $\nu_\mu$, and $\nu_\tau$ to the $Z$ boson. Our results justify the assumption of universality in these couplings that is usually made, as for example in the analysis of solar neutrinos detected at SNO.Comment: 8 pages, no figures. A few comments added. It matches version to be published in PR

Constraints on Neutrino Parameters from Neutral-Current Solar Neutrino Measurements

We generalize the pull approach to define the $\chi^2$ function to the analysis of the data with correlated statistical errors. We apply this method to the analysis of the Sudbury Neutrino Collaboration data obtained in the salt-phase. In the global analysis of all the solar neutrino and KamLAND data we find the best fit (minimum $\chi^2$) values of neutrino parameters to be $\tan^2 \theta_{12} \sim 0.42$ and $\delta m_{12}^2 \sim 7.1 \times 10^{-5}$ eV$^2$. We confirm that the maximal mixing is strongly disfavored while the bounds on $\delta m_{12}^2$ are significantly strengthened.Comment: 6 figures. Some typos are corrected, figures are visually improve

Results from K2K and status of T2K

Results from the K2K experiment and status of the T2K experiment are reported.Comment: 9 pages, 6 figures. Talk at International Conference on New Trends in High-Energy Physics (Crimea2005), Yalta, Ukraine, September 10-17, 200

The Majorana Neutrino Mass Matrix with One Texture Zero and One Vanishing Eigenvalue

Possible patterns of the Majorana neutrino mass matrix $M$ with one texture zero and one vanishing eigenvalue are classified and discussed. We find that three one-zero textures of $M$ with $m_1 =0$ and four one-zero textures of $M$ with $m_3 =0$ are compatible with current neutrino oscillation data. The implications of these phenomenological ans$\rm\ddot{a}$tze on the neutrino mass spectrum and the neutrinoless double beta decay are also explored in some detail.Comment: RevTex 10 pages (with 2 PS figues). More discussions and references adde

Lepton Flavour Violation in a Class of Lopsided SO(10) Models

A class of predictive SO(10) grand unified theories with highly asymmetric mass matrices, known as lopsided textures, has been developed to accommodate the observed mixing in the neutrino sector. The model class effectively determines the rate for charged lepton flavour violation, and in particular the branching ratio for $\mu -> e \gamma$, assuming that the supersymmetric GUT breaks directly to the constrained minimal supersymmetric standard model (CMSSM). We find that in light of the combined constraints on the CMSSM parameters from direct searches and from the WMAP satellite observations, the resulting predicted rate for $\mu -> e \gamma$ in this model class can be within the current experimental bounds for low $\tan \beta$, but that the next generation of $\mu -> e \gamma$ experiments would effectively rule out this model class if LFV is not detected.Comment: 23 page

Asymmetric neutrino emission due to neutrino-nucleon scatterings in supernova magnetic fields

We derive the cross section of neutrino-nucleon scatterings in supernova magnetic fields, including weak-magnetism and recoil corrections. Since the weak interaction violates the parity, the scattering cross section asymmetrically depends on the directions of the neutrino momenta to the magnetic field; the origin of pulsar kicks may be explained by the mechanism. An asymmetric neutrino emission (a drift flux) due to neutrino-nucleon scatterings is absent at the leading level of $\mathcal O(\mu_BB/T)$, where $\mu_B$ is the nucleon magneton, $B$ is the magnetic field strength, and $T$ is the matter temperature at a neutrinosphere. This is because at this level the drift flux of the neutrinos are exactly canceled by that of the antineutrinos. Hence, the relevant asymmetry in the neutrino emission is suppressed by much smaller coefficient of $\mathcal O(\mu_BB/m)$, where $m$ is the nucleon mass; detailed form of the relevant drift flux is also derived from the scattering cross section, using a simple diffusion approximation. It appears that the asymmetric neutrino emission is too small to induce the observed pulsar kicks. However, we note the fact that the drift flux is proportional to the deviation of the neutrino distribution function from the value of thermal equilibrium at neutrinosphere. Since the deviation can be large for non-electron neutrinos, it is expected that there occurs cancellation between the deviation and the small suppression factor of $\mathcal O(\mu_BB/m)$. Using a simple parameterization, we show that the drift flux due to neutrino-nucleon scatterings may be comparable to the leading term due to beta processes with nucleons, which has been estimated to give a relevant kick velocity when the magnetic field is sufficiently strong as $10^{15}$--$10^{16}$ G.Comment: 19 pages, 1 figure. Accepted by Physical Review

Measuring CP violation and mass ordering in joint long baseline experiments with superbeams

We propose to measure the CP phase $\delta_{\rm CP}$, the magnitude of the neutrino mixing matrix element $|U_{e3}|$ and the sign of the atmopheric scale mass--squared difference $\Delta{\rm m}^2_{31}$ with a superbeam by the joint analysis of two different long baseline neutrino oscillation experiments. One is a long baseline experiment (LBL) at 300 km and the other is a very long baseline (VLBL) experiment at 2100 km. We take the neutrino source to be the approved high intensity proton synchrotron, HIPA. The neutrino beam for the LBL is the 2-degree off-axis superbeam and for the VLBL, a narrow band superbeam. Taking into account all possible errors, we evaluate the event rates required and the sensitivities that can be attained for the determination of $\delta_{\rm CP}$ and the sign of $\Delta m^2_{31}$. We arrive at a representative scenario for a reasonably precise probe of this part of the neutrino physics.Comment: 25 RevTEX pages, 16 PS figures, revised figure captions and references adde

Homestake result, sterile neutrinos and low energy solar neutrino experiments

The Homestake result is about ~ 2 \sigma lower than the Ar-production rate, Q_{Ar}, predicted by the LMA MSW solution of the solar neutrino problem. Also there is no apparent upturn of the energy spectrum (R \equiv N_{obs}/N_{SSM}) at low energies in SNO and Super-Kamiokande. Both these facts can be explained if a light, \Delta m^2_{01} ~ (0.2 - 2) \cdot 10^{-5} eV^2, sterile neutrino exists which mixes very weakly with active neutrinos: \sin^2 2\alpha ~ (10^{-5} - 10^{-3}). We perform both the analytical and numerical study of the conversion effects in the system of two active neutrinos with the LMA parameters and one weakly mixed sterile neutrino. The presence of sterile neutrino leads to a dip in the survival probability in the intermediate energy range E = (0.5 - 5) MeV thus suppressing the Be, or/and pep, CNO as well as B electron neutrino fluxes. Apart from diminishing Q_{Ar} it leads to decrease of the Ge-production rate and may lead to decrease of the BOREXINO signal and CC/NC ratio at SNO. Future studies of the solar neutrinos by SNO, SK, BOREXINO and KamLAND as well as by the new low energy experiments will allow us to check this possibility. We present a general analysis of modifications of the LMA energy profile due to mixing with new neutrino states.Comment: Figures 5 and 6 modified, shorter version will be published in PR

Solar neutrino oscillations and indications of matter effects in the Sun

Assuming the current best-fit solutions to the solar neutrino problem at large mixing angle, we briefly illustrate how prospective data from the Sudbury Neutrino Observatory (SNO) and from the Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) can increase our confidence in the occurrence of standard matter effects on active neutrino flavor oscillations in the Sun, which are starting to emerge from current data.Comment: Updated to include the first KamLAND data. One figure adde

Implications of the KamLAND Measurement on the Lepton Flavor Mixing Matrix and the Neutrino Mass Matrix

We explore some important implications of the KamLAND measurment on the lepton flavor mixing matrix $V$ and the neutrino mass matrix $M$. The model-independent constraints on nine matrix elements of $V$ are obtained to a reasonable degree of accuracy. We find that nine two-zero textures of $M$ are compatible with current experimental data, but two of them are only marginally allowed. Instructive predictions are given for the absolute neutrino masses, Majorana phases of CP violation, effective masses of the tritium beta decay and neutrinoless double beta decay.Comment: RevTex 15 pages (4 PS figures included