Tau neutrino mass from semileptonic decays

The semileptonic three particle decays of the tau provide determinations of the tau neutrino mass. The shift of the maximal energy of the observable final state particles islinear in the neutrino mass. The endpoint energy of the pion and a partially integrated decay rate in τ → πωv _τ and τ → πρV _τ are sensitive to a neutrino mass smaller than 100 MeV. Thus, the present bound on \(m_{v_\tau } \) can significantly be improved.     

The electroweak mixing angle in unified gauge theories

We study in detail the factors that influence the unification relations among the coupling parameters of strong and electroweak interactions. We find that the factor that decides the unification relations in a theory is the fermion content of the theory. The specific ‘observed’ group of strong and electroweak interactions used and the specific unification group in which these interactions are embedded are largely irrelevant. In particular, we find that the unification value of the electroweak mixing angle is the same for almost all models of interest. We also explicitly illustrate that the canonical value 3/8 of the mixing angle is a characteristic result of the currently popular sequential doublets scheme of fermions. Addition of extra fermion singlets reduces the mixing angle to 1/4. We propose this sequential triplets scheme of fermions as an interesting alternative to the current scheme.     

Measuring the 13 neutrino mixing angle and the CP phase with neutrino telescopes

The observed excess of high-energy cosmic rays from the Galactic plane in the energy range around 10(18) eV may be explained by neutron primaries generated in the photodissociation of heavy nuclei. In this scenario, lower-energy neutrons decay before reaching the Earth and produce a detectable flux in a 1 km(3) neutrino telescope. The initial flavor composition of the neutrino flux, phi(nu(e)):phi(nu(mu)):phi(nu(tau))=1:0:0, permits a combined nu(mu)/nu(tau) appearance and nu(e) disappearance experiment. The observable flux ratio phi(nu(mu))/phi(nu(e)+nu(tau) at Earth depends on the 13 mixing angle theta(13) and the leptonic CP phase delta(CP), thus opening a new way to measure these two quantities.     

Group-Theoretic analysis of the mixing angle in the electroweak gauge group

In this paper we provide strong mathematical support for the idea that the experimentally measured magnitude 1 –M _W ² /M _Z ² associated with sin² _W in the standard model of electroweak interactions cannot be simultaneously identified with the squared quotient of the electric charge by theSU(2) charge,e ²/g ². In fact, the natural, mathematical requirement that the Weinberg rotation between the gauge fields associated with the third component of the weak isospin (T ₃) and the hypercharge (Y) proceeds from aglobal Lie-group homomorphism of theSU(2) U(l) _Y gauge group in some locally isomorphic Lie group [which then proves to beU(2)], and not from alocal (Lie algebra)isomorphism, imposes strong restrictions so as to fix the single valuee ²/g ²=1/2. The two definitions of sin² _W can only be identified in the asymptotic limit corresponding to an earlier stage of the universe before the spontaneous symmetry breaking had taken place.     

Parton structure of the nucleon and precision determination of the weinberg angle in neutrino scattering

A next-to-leading-order (NLO) calculation of neutrino cross sections, including power-suppressed mass terms, is used to evaluate the Paschos-Wolfenstein ratio, in order to better assess the validity and significance of the NuTeV anomaly. We study the shift of sin2thetaW obtained in calculations with parton distribution function sets that allow s(x) not = s(x), enabled by recent neutrino dimuon data from CCFR and NuTeV. The extracted value of sin2thetaW is closely correlated with the strangeness asymmetry. Taken together with recent developments of possible isospin violation and electroweak effects, our results suggest that the new dimuon data, the Weinberg angle measurement, and other data sets used in global QCD parton structure analysis can all be consistent within the standard model. A full NLO analysis of the actual experimental measurement will help to clarify this issue further.     

Two-texture zeros and near-maximal atmospheric neutrino mixing angle

We study the implications of a large value of the effective Majorana neutrino mass for a class of two-texture zero neutrino mass matrices in the flavour basis. We find that these textures predict near-maximal atmospheric neutrino mixing angle in the limit of large effective Majorana neutrino mass. We present the symmetry realization of these textures using the discrete cyclic group Z₃. It is found that the texture zeros realized in this work remain stable under the renormalization group running of the effective neutrino mass matrix at one-loop level.     

The electroweak mixing angle in unified gauge theories—the renormalisation effects

A general analysis of the renormalisation corrections to the unification results for the coupling constants of strong and electroweak interactions is attempted. In particular, the effects of introducing an energy scale intermediate between the unification energy and the low-energy regions are studied and found to be important. This analysis is applied to unification schemes of both kinds, namely, unification at superhigh energies, and unification at accessible energies.     

Precise determination of electroweak parameters in neutrino-nucleon scattering

The NuTeV Collaboration has extracted the electroweak parameter sin(2)theta(W) from the measurement of the ratios of neutral current to charged current nu and (-)nu cross sections. Our value, sin(2)theta((on-shell))(W) = 0.2277 +/- 0.0013(stat) +/- 0.0009(syst), is 3 standard deviations above the standard model prediction. We also present a model independent analysis of the same data in terms of neutral-current quark couplings.     

Contraction of electroweak model and neutrino

The electroweak model, which lepton sector correspond to the contracted gauge group SU(2; j) × U(1), j ?? 0, whereas boson and quark sectors are standard one, is suggested. The field space of the model is fibered under contraction in such a way that neutrino fields are in the fiber and all other fields are in the base. Properties of the fibered field space are understood in context of semi-Riemannian geometry. This model describes in a natural manner why neutrinos so rarely interact with matter, as well as why neutrino cross section increase with the energy. Dimensionfull parameter of the model is interpreted as neutrino energy. Dimensionless contraction parameter j at low energy is connected with the Fermi constant of weak interactions and is approximated as j ² ?? 10^?5.     

Impact of large mixing angle MSW solution on neutrino mass matrix

We have discussed the quark-lepton mass matrices with the U(1) and O(3) flavor symmetry in SU(5), which lead to the large mixing angle MSW solution of solar neutrinos.     

Determining horizontal symmetry from neutrino mixing

We argue that the best way to determine horizontal symmetry is from neutrino mixing and proceed to show that the only finite group capable of yielding the tribimaximal mixing for all Yukawa couplings is S4, or any group containing it. The method used is largely group theoretical, but it can be implemented by dynamical schemes in which the Higgs expectation values introduced to break S4 spontaneously are uniquely determined up to an unknown scale for each.     

A horizontal model for neutrino mixing

We consider a horizontal SU(3)_H × SU(2)_L × U(1) model in which the large Majorana neutrino masses are associated with a large horizontal scale. We find that the charged lepton sector is responsible for the neutrino mixing which we calculate in the present model. We also find that the neutrino oscillation length is related to the horizontal scale.     

Maximal atmospheric neutrino mixing from texture zeros and quasi-degenerate neutrino masses

It is well known that, in the basis where the charged-lepton mass matrix is diagonal, there are seven cases of two texture zeros in Majorana neutrino mass matrices that are compatible with all experimental data. We show that two of these cases, namely B₃ and B₄ in the classification of Frampton, Glashow and Marfatia, are special in the sense that they automatically lead to near-maximal atmospheric neutrino mixing in the limit of a quasi-degenerate neutrino mass spectrum. This property holds true irrespective of the values of the solar and reactor mixing angles because, for these two cases, in the limit of a quasi-degenerate spectrum, the second and third row of the lepton mixing matrix are, up to signs, approximately complex-conjugate to each other. Moreover, in the same limit the aforementioned cases also develop a maximal CP-violating CKM-type phase, provided the reactor mixing angle is not too small.