IMPLICATIONS OF SYMMETRY BREAKING AND PHENOMENOLOGY FOR SUPERSTRING-BASED MODELS WITH GAUGE SYMMETRY SU(3)C × SU(2)L × SU(2) × U(1) × U(1)′

Abstract

We discuss symmetry breaking and phenomenological aspects of rank 6 effective models in 4 dimensions, suggested by Calabi-Yau compactification of the heterotic E8 × E8 superstring, which have gauge group SU (3)C × SU (2)L × SU (2) × U (1) × U (1)′. The simplest and most natural form of electroweak symmetry breaking for the softly broken effective SUSY theory is considered, and only those additions and alterations to the 273 based superpotential necessary to eliminate phenomenological problems are made. There are two physically distinct additional SU(2) factors, SU (2)N and SU (2)R. The former has all gauge bosons electrically neutral, the latter both charged and neutral. The additional SU(2) symmetry implies that large Dirac neutrino masses must be eliminated by a see-saw mechanism requiring the introduction of an E6 singlet per generation and an intermediate scale of symmetry breaking MI(≥ 1010 GeV ). The intermediate scale symmetry breaking together with the couplings involving E6 singlets needed for the see-saw mechanism unambiguously determines the form of the superpotential describing physics at low scales ≤ 1 TeV . All additional heavy charge [Formula: see text] quarks and additional Higgs doublets have masses ≤ 1 TeV . An additional U (1)E remains unbroken down to the 1 TeV scale. The resulting effective theories have no U (1)E mediated FCNC due to mixing of heavy and light charge [Formula: see text] quarks. Some couplings must be eliminated in order to prevent rapid nucleon decay. For the 3 generation SU (2)N model the value of sin 2 θω is low but compatible with the range permitted for a model with an extra U (1)E. 4 generation SU (2)N and SU (2)R models are generally ruled out by sin 2 θω. For the SU (2)R models there are two cases depending on whether SU (2)R is broken at M1 or remains unbroken down to the 1 TeV scale. The latter case is ruled out by large sin 2 θω. The former case has acceptable sin 2 θω but is ruled out by large [Formula: see text] mass splitting, leaving only SU (2)N models as a possibility. The SU (2)N symmetry implies that the electron gains a mass either from 1-loop corrections involving heavy charge [Formula: see text] quarks or by more than one pair of Higgs doublets gaining an expectation value. The former can readily generate the correct magnitude of electron mass, but requires suppression of couplings of down-type quarks to additional Higgs doublets by a factor ≥ 102 cf. the Yukawa couplings responsible for quark and lepton masses in order to prevent rapid µ → eγ. It is shown that the SU (2)N model has no possibility of explaining baryogenesis by out of equilibrium particle decays. Flat directions necessary for the Affleck-Dine mechanism of baryogenesis exist only if additional conditions are imposed on the superpotential.