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Physics implications of perturbative string vacua

By Jing Wang


A systematic investigation of the phenomenology of a class of perturbative string models is presented. We first analyze perturbative heterotic superstring models which have the gauge group and particle content of the minimal supersymmetric standard model (MSSM). The presence of the anomalous U(1), which is generic in this class of superstring models, leads to the generation of a nonzero Fayet-Iliopoulos (FI) term that triggers a number of scalar fields to acquire vacuum expectation values along flat directions, leading to a supersymmetric restabilized string vacuum. We concentrate on the physics implications along the D- and F-flat directions of the restabilized vacuum, which involve the determination of the reduced gauge structure and the calculation of the complete set of effective mass terms and trilinear couplings. For a class of flat directions of a prototype quasi-realistic free fermionic model (CHL5), we present, a detailed analysis of the phenomenological implications of the massless spectrum and the effective trilinear couplings. The issues considered include the phenomenological consequences of massless exotic particles, the low energy predictions for the gauge couplings, possible fermion textures, the presence of baryon- and lepton-number violating processes, possible R-parity violation, and non-canonical μ terms. We then introduce soft supersymmetry breaking parameters into the model and utilize the renormalization group equations to determine the radiative breaking of the gauge symmetry, which for this class of flat directions includes an additional U(1) ′ symmetry along with the electroweak symmetry. We specifically study scenarios with a phenomenologically acceptable Z − Z′ hierarchy. We find that the fermion mass spectrum is not fully realistic. An extended Higgs sector is required and there are massless or ultralight Higgs, charginos, and neutralinos due to the presence of a limited number of non-canonical effective μ terms. Finally, we turn to a study of perturbative Type I superstring models from orientifold constructions. Although model-building techniques are not as sophisticated as in the perturbative heterotic case and there is no model with the gauge structure and particle content of the MSSM, these models exhibit distinctive features in terms of the number of the anomalous U(1)\u27s and the associated FI terms For the specific case of the Z 3 orientifold (ABPSS), we study the anomaly cancellation associated with the anomalous U(1), determine the form of the FI term, and investigate possible corrections to the gauge couplings (which turn out to vanish). We investigate the phenomenological implications of blowing up the Z3 orientifold, which induces a nonzero FI term for the anomalous U(1). We construct the (non-Abelian) D- and F-flat directions of the model, and determine the surviving gauge groups and the mass, spectra of the restabilized vacua

Topics: Particle physics
Publisher: ScholarlyCommons
Year: 1999
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Provided by: ScholarlyCommons@Penn
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