Large Mixing and CP Violation in Neutrino Oscillations

I introduce a simple phenomenological model of lepton flavor mixing and CP violation based on the flavor democracy of charged leptons and the mass degeneracy of neutrinos. The nearly bi-maximal mixing pattern, which can interpret current data on atmospheric and solar neutrino oscillations, emerges naturally from this model. The rephasing-invariant strength of CP or T violation amounts to about one percent and could be measured in the long-baseline neutrino experiments. The similarity and difference between lepton and quark flavor mixing phenomena are also discussed.Comment: LaTex 6 pages. Talk given at the Sixth Topical Seminar on Neutrino and Astroparticle Physics, San Miniato, Italy, May 1999 (To appear in the Proceedings Supplements of Nucl. Phys. B

Wavefunction-Independent Relations between the Nucleon Axial-Coupling g_A and the Nucleon Magnetic Moments

We calculate the proton's magnetic moment $\mu_p$ and its axial-vector coupling $g_A$ as a function of its Dirac radius $R_1$ using a relativisitic three-quark model formulated on the light-cone. The relationship between $\mu_p$ and $g_A$ is found to be independent of the assumed form of the light-cone wavefunction. At the physical radius $R_1=0.76$ fm, one obtains the experimental values for both $\mu_p$ and $g_A$, and the helicity carried by the valence $u$ and $d$ quarks are each reduced by a factor $\simeq 0.75$ relative to their non-relativistic values. At large proton radius, $\mu_p$ and $g_A$ are given by the usual non-relativistic formulae. At small radius, $\mu_p$ becomes equal to the Dirac moment, as demanded by the Drell-Hearn-Gerasimov sum rule. In addition, as $R_1 \to 0,$ the constituent quark helicities become completely disoriented and $g_A \to 0$.Comment: 17 pages, RevTeX, 4 uuencoded figures, SLAC-PUB-643

Complete Cubic and Quartic Couplings of 16 and 16ˉ\bar {16} in SO(10) Unification

A recently derived basic theorem on the decomposition of SO(2N) vertices is used to obtain a complete analytic determination of all SO(10) invariant cubic superpotential couplings involving $16_{\pm}$ semispinors of SO(10) chirality $\pm$ and tensor representations. In addition to the superpotential couplings computed previously using the basic theorem involving the 10, 120 and $\bar{126}$ tensor representations we compute here couplings involving the 1, 45 and 210 dimensional tensor representations, i.e., we compute the $\bar{16}_{\mp}16_{\pm}1$,$\bar{16}_{\mp}16_{\pm}45$ and $\bar{16}_{\mp}16_{\pm}210$ Higgs couplings in the superpotential. A complete determination of dimension five operators in the superpotential arising from the mediation of the 1, 45 and 210 dimensional representations is also given. The vector couplings $\bar{16}_{\pm}16_{\pm}1$, $\bar{16}_{\pm}16_{\pm}45$ and $\bar{16}_{\pm}16_{\pm}210$ are also analyzed. The role of large tensor representations and the possible application of results derived here in model building are discussed.Comment: 21 pages, Latex. Revised version to appear in Nuclear Physics

Coupling the Supersymmetric 210 Vector Multiplet to Matter in SO(10)

An analysis of the couplings of the 210 dimensional SO(10) vector multiplet to matter is given. Specifically we give an $SU(5)\times U(1)$ decomposition of the vector couplings $\bar{16}_{\pm}-16_{\pm}-210$, where $16_{\pm}$ is the semispinor of SO(10) chirality ${\pm}$, using a recently derived basic theorem. The analysis is carried out using the Wess-Zumino gauge. However, we also consider the more general situation where all components of the vector multiplet enter in the couplings with the chiral fields. Here elimination of the auxiliary fields leads to a sigma model type nonlinear Lagrangian. Interactions of the type analysed here may find applications in effective theories with the 210 vector arising as a condensate. The analysis presented here completes the explicit computation of all lowest order couplings involving the $16_{\pm}$ of spinors with Higgs and vectors multiplets using the basic theorem.Comment: 33 pages, Latex. To appear in Nuclear Physics

An apprach to generate large and small leptonic mixing angles

We take up the point of view that Yukawa couplings can be either 0 or 1, and the mass patterns of fermions are generated purely from the structure of the Yukawa matrices. We utilize such neutrino as well as charged leptonic textures which lead to (maximal) mixing angles of $\pi/4$ in each sector for relevant transitions. The combined leptonic CKM mixing angles are $\pi/4 \pm \pi/4$ which lead to very small $\sin^2 2 \Theta$ relevant to solar neutrino and LSND experiments. We propose that on the other hand the absence of the charged leptonic partner of the sterile neutrino maintains the angle $\pi/4$ from the neutrino sector for the transition $\nu_\mu \leftrightarrow \nu_s$ and hence atmospheric neutrino anomaly is explained through maximal mixing

Energy Losses (Gains) of Massive Coloured Particles in Stochastic Colour Medium

The propagation of massive coloured particles in stochastic background chromoelectric field is studied using the semiclassical equations of motion. Depending on the nature of the stochastic background we obtain the formulae for the energy losses of heavy coloured projectile in nonperturbative hadronic medium and for the energy gains in the stochastic field present, e.g., in the turbulent plasma. The result appears to be significantly dependent on the form of the correlation function of stochastic external fieldComment: 9 pages, BI-TP 94/15, plain LaTe

Analysis of Couplings with Large Tensor Representations in SO(2N) and Proton Decay

We develop techniques for the analysis of SO(2N) invariant couplings which allow a full exhibition of the SU(N) invariant content of the spinor and tensor representations. The technique utilizes a basis consisting of a specific set of reducible SU(N) tensors in terms of which the SO(2N) invariant couplings have a simple expansion. The technique is specially useful for couplings involving large tensor representations. We exhibit the technique by performing a complete determination of the trilinear couplings in the superpotential for the case of SO(10) involving the 16 plet of matter, i.e., we give a full determination of the ${16-16-10_s}$, ${16-16-120_a}$ and ${16-16-\bar{126}_s}$ couplings. The possible role of large tensor representations in the generation of quark lepton textures is discussed. It is shown that the couplings involving $\bar{126}$ dimensional representation generate extra zeros in the Higgs triplet textures which can lead to an enhancement of the proton decay lifetime by a factor of $10^3$. These results also have implications for neutrino mass textures.Comment: 14 pages, Latex: With the corrections of an Erratum included in the text of pape

New Supersymmetric Contributions to t−>cVt->cV

We calculate the electroweak-like one-loop supersymmetric contributions to the rare and flavor-violating decay of the top quark into a charm quark and a gauge boson: $t->c V$, with $V=\gamma,Z,g$. We consider loops of both charginos and down-like squarks (where we identify and correct an error in the literature) and neutralinos and up-like squarks (which have not been calculated before). We also account for left-right and generational squark mixing. Our numerical results indicate that supersymmetric contributions to $t->cV$ can be upto 5 orders of magnitude larger than their Standard Model counterparts. However, they still fall short of the sensitivity expected at the next-generation top-quark factories.Comment: 13 pages, LaTex, 1 figure included. Final version to appear in Physical Review D. Chargino contribution dealt with in greater detail. Minor revisions in tex

SU(3) Mixing for Excited Mesons

The SU(3)-flavor symmetry breaking and the quark-antiquark annihilation mechanism are taken into account for describing the singlet-octet mixing for several nonets assigned by Particle Data Group(PDG). This task is approached with the mass matrix formalism