Light Dirac neutrino in left-right-symmetric models.
Recent experiments related to neutrino mass and neutrinoless double-..beta.. decay suggest that the electron neutrino is a Dirac particle with its mass of the order of 10--20 eV. In most of the existing grand-unified scenarios neutrinos turn out to be Majorana particles, unless an arbitrarily small Yukawa coupling and/or Higgs-field vacuum expectation value is introduced. In this paper we propose a model where one can readily accommodate an ultralight Dirac neutrino. It has been pointed out that any left-right-symmetric model with a second set of heavier fermions can have an ultralight Dirac neutrino, if the global symmetry which prevents any mixing between the two sets of fermions allows a mixing between antifermions and the heavier fermion. The complete potential has been minimized to obtain the mass matrix. It is shown that the required symmetry-breaking mass scales for the present case are consistent with low-energy values of sinX sup 2 theta sub w: and ..cap alpha../sub s/.

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: 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: 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: 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: Rapidity distribution of photons emitted from a hadronizing quark-gluon plasma.
abstract: The rapidity distribution of thermal photons emitted from a hadronizing quark-gluon plasma is obtained with initial conditions locally determined from the hadronic rapidity density and assuming a longitudinal scaling expansion as in Bjorken hydrodynamics. The corresponding results for direct (QCD) photons and for decay photons are also obtained. The rapidity distributions of the three types of photons are found to be quite different and may help identify the most favorable window in the momentum space for identification for the quark-gluon plasma