216 research outputs found

### 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

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