Physics implications of flat directions in free fermionic superstring models. II. Renormalization group analysis - art. no. 115003

We continue the investigation of the physics implications of a class of hat directions for a prototype quasi-realistic free fermionic string model (CH L5), building upon the results of a previous paper in which the complete ma ss spectrum and effective trilinear couplings of the observable sector were calculated to all orders in the superpotential. We introduce soft supersym metry breaking mass parameters into the model, and investigate the gauge sy mmetry breaking patterns and the renormalization group analysis for two rep resentative hat directions, which leave an additional U(1)' as well as the SM gauge group unbroken at the string scale. We study symmetry breaking pat terns that lead to a phenomenologically acceptable Z-Z' hierarchy, M-Z' sim ilar to O(1 TeV) and 10(12) GeV for electroweak and intermediate scale U(1) ' symmetry breaking, respectively, and the associated mass spectra after el ectroweak symmetry breaking. The fermion mass spectrum exhibits unrealistic features, including massless exotic fermions, but has an interesting d-qua rk hierarchy and associated CKM matrix in one case. There are (some) non-ca nonical effective mu terms, which lead to a non-minimal Higgs sector with m ore than two Higgs doublets involved in the symmetry breaking, and a rich s tructure of Higgs particles, charginos, and neutralinos, some of which, how ever, are massless or ultralight. In the electroweak scale cases the scale of supersymmetry breaking is set by the Z' mass, with the sparticle masses in the several TeV range. [S0556-2821(99)06109-3].