Discriminating horizontal symmetries from operator analysis and proton-decay experiments.
The impact of different horizontal symmetries on nucleon decay is discussed within the framework of the standard and the left-right-symmetric theory. Under very general assumptions of operator analysis, it is demonstrated that U(1)/sub H/, SU(2)/sub H/, SU(3)/sub H//sup V/L, and SU(3)/sub H//sup V/ symmetries predict different nucleon decay modes and, hence, the on-going proton-decay experiments can be used to discriminate among the different horizontal symmetries. Furthermore, it is shown that, under favorable situations, the standard and the left-right-symmetric theory can also be distinguished.

title: Degenerate Dirac neutrinos
abstract: A simple extension of the standard model is proposed in which all the three generations of neutrinos are Dirac particles and are naturally light. We then assume that the neutrino mass matrix is diagonal and degenerate, with a few eV mass to solve the dark matter problem. The self-energy radiative corrections, however, remove this degeneracy and allow mixing of these neutrinos. The electroweak radiative corrections then predict a lower bound on the ν μ -ν e mass difference which solves the solar neutrino problem through the MSW mechanism and also predict a lower bound on the ν τ -ν μ mass difference which is just enough to explain the atmospheric neutrino problem as reported by Super-Kamiokande.

title: Superunified model with naturally ultralight dirac neutrinos
abstract: The recently proposed mechanism to naturally generate one ultralight Dirac neutrino per fermion family is implemented by construction of a globally supersymmetric SO(10) GUT superpotential featuring geometric hierarchy. A step forward is thus taken towards providing a firm theoretical basis for the relation m ν = O (m 3 2 )M SUSY /M GUT .

title: ANOMALY FOR MODEL BUILDING
abstract: A simple algorithm to calculate the group theory factor entering in anomalies at four and six dimensions for SU(N) and SO(N) groups in terms of the Casimir invariants of their subgroups is presented. Explicit examples of some of the lower dimensional representations of SU(n), n ≤ 5 and SO(10) groups are presented, which could be used for model building in four and six dimensions.

title: Neutrino dark energy in grand unified theories
abstract: We studied a left-right symmetric model that can accommodate the neutrino dark energy (νDE) proposal. The type-III seesaw mechanism is implemented to give masses to the neutrinos. After explaining the model, we study the consistency of the model by minimizing the scalar potential and obtaining the conditions for the required vacuum expectation values of the different scalar fields. This model is then embedded in an SO(10) grand unified theory and the allowed symmetry breaking scales are determined by the condition of the gauge coupling unification. Although SU(2) R breaking is required to be high, its Abelian subgroup U(1) R is broken in the TeV range, which can then give the required neutrino masses and predicts new gauge bosons that could be detected at LHC. The neutrino masses are studied in detail in this model, which shows that at least 3 singlet fermions are required.

title: Magnetic moments and the structure function of the proton
abstract: The EMC collaboration have reported a measurement of the proton structure function which has been interpreted to mean that the spin of the proton is not predominantly that of the quarks (ΔΣ=Δμ+Δd+Δs=0.13±0.19). We show that the magnetic moments of the baryons are independent of this measurement and are given (within 10-20%) for a range of ΔΣ including the valence model value ΔΣ=1. The magnetic moments of the quarks can only be fixed if the quantity ΔΣ is determined very accurately.

title: No crisis for big bang nucleosynthesis.
abstract: Contrary to a recent claim, the inferred primordial abundances of the light elements are quite consistent with the expectations from standard big bang nucleosynthesis when attention is restricted to direct observations rather than results from chemical evolution models. The number of light neutrino (or equivalent particle) species (N�) can be as high as 4.53 if the nucleon-tophoton ratio (�) is at its lower limit of 1.65 × 10 −10 , as constrained by the upper bound on the deuterium abundance in high redshift quasar absorption systems. Alternatively, with N� = 3, � can be as high as 8.90 × 10 −10 if the deuterium abundance is bounded from below by its interstellar value.