Physics Implications of Precision Electroweak Experiments

A brief review is given of precision electroweak physics, and its implications for establishing the standard model and constraining the possibilities for new physics at the TeV scale and beyond

Implications of Solar and Atmospheric Neutrinos

The importance of non-zero neutrino mass as a probe of particle physics, astrophysics, and cosmology is emphasized. The present status and future prospects for the solar and atmospheric neutrinos are reviewed, and the implications for neutrino mass and mixing in 2, 3, and 4-neutrino schemes are discussed. The possibilities for significant mixing between ordinary and light sterile neutrinos are described

The 331 model with right-handed neutrinos

We explore some more consequences of the $SU(3)_L\otimes U(1)_N$ electroweak model with right-handed neutrinos. By introducing the $Z - Z'$ mixing angle $\phi$, the {\it exact} physical eigenstates for neutral gauge bosons are obtained. Because of the mixing, there is a modification to the $Z^1$ coupling proportional to $\sin\phi$. The data from the $Z$-decay allows us to fix the limit for $\phi$ as $-0.0021 \leq \phi \leq 0.000132$. >From the neutrino neutral current scatterings, we estimate a bound for the new neutral gauge boson $Z^2$ mass in the range 300 GeV, and from symmetry-breaking hierarchy a bound for the new charged and neutral (non-Hermitian) gauge bosons $Y^{\pm}, X^o$ are obtained.Comment: Slight changes in section 5, Latex, 16 page

Domain Walls in SU(5)

We consider the Grand Unified SU(5) model with a small or vanishing cubic term in the adjoint scalar field in the potential. This gives the model an approximate or exact Z$_2$ symmetry whose breaking leads to domain walls. The simplest domain wall has the structure of a kink across which the Higgs field changes sign ($\Phi \to -\Phi$) and inside which the full SU(5) is restored. The kink is shown to be perturbatively unstable for all parameters. We then construct a domain wall solution that is lighter than the kink and show it to be perturbatively stable for a range of parameters. The symmetry in the core of this domain wall is smaller than that outside. The interactions of the domain wall with magnetic monopole is discussed and it is shown that magnetic monopoles with certain internal space orientations relative to the wall pass through the domain wall. Magnetic monopoles in other relative internal space orientations are likely to be swept away on collision with the domain walls, suggesting a scenario where the domain walls might act like optical polarization filters, allowing certain monopole ``polarizations'' to pass through but not others. As SU(5) domain walls will also be formed at small values of the cubic coupling, this leads to a very complicated picture of the evolution of defects after the Grand Unified phase transition.Comment: 6 pages, 1 figure. Animations can be viewed at http://theory4.phys.cwru.edu/~levon/figures.htm

An SU(5)⊗\otimesZ_{13} Grand Unification Model

We propose an SU(5) grand unified model with an invisible axion and the unification of the three coupling constants which is in agreement with the values, at $M_Z$, of $\alpha$, $\alpha_s$, and $\sin^2\theta_W$. A discrete, anomalous, $Z_{13}$ symmetry implies that the Peccei-Quinn symmetry is an automatic symmetry of the classical Lagrangian protecting, at the same time, the invisible axion against possible semi-classical gravity effects. Although the unification scale is of the order of the Peccei-Quinn scale the proton is stabilized by the fact that in this model the standard model fields form the SU(5) multiplets completed by new exotic fields and, also, because it is protected by the $Z_{13}$ symmetry.Comment: 14 pages, more typos correcte