Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)




Marc Sher


We consider the effective low-energy SU(2) L x SU(2)I x U(1)Y x U(1)Y' model, which is based on the E6 grand unification theory. SU(2)I is a subgroup of SU(3) R and commutes with the electric charge operator.;Higgs bosons in the Standard Model and two-Higgs doublet models are reviewed and studied first. The flavor-changing neutral currents and their effects on the anomalous magnetic moment of the muon are discussed. Bounds on masses of Higgs bosons are obtained by requiring that the vacuum is stable and perturbation theory is valid up to a large scale. We introduce Higgs multiplets including two neutral doublets to break down SU(2)L x SU(2)I x U(1)Y x U(1) Y' to U(1) em. An upper bound of about 150 GeV to the lightest neutral Higgs scalar mass is found.;The gauge bosons corresponding to SU(2) I are charge-neutral. Production and effects of W I bosons are reviewed first. Mixings among neutral gauge bosons appear naturally. Electroweak precision experiments, including Z-pole experiments, mW measurements and low-energy neutral current experiments are used to put indirect constraints on masses of the extra neutral gauge bosons and the mixings between them and the ordinary Z boson. We also consider the possible constraint from a proposed measurement at Jefferson Lab of the proton's weak charge. It is found that the mixing angles are very small, namely ;theta; ≤ 0.005. The lower bound for the mass of the lightest extra neutral gauge boson is found to be about 560--800 GeV, which is comparable with the current direct search limit. Low-energy neutral current experiments give the strongest bounds on the lightest extra neutral gauge boson.;Fermions reside in the 27 fundamental representation of E6. We study the pair production of heavy charged exotic leptons at e+e- colliders in this model. In addition to the standard gamma and Z boson contributions, a t-channel contribution due to WI-boson exchange, which is unsuppressed by mixing angles, is quite important. We calculate the cross section, the left-right and forward-backward asymmetries, and discuss how to differentiate different models.



© The Author

Included in

Physics Commons