A Minimal Superstring Standard Model II: A Phenomenological Study

Recently, we demonstrated the existence of heterotic--string solutions in which the observable sector effective field theory just below the string scale reduces to that of the MSSM, with the standard observable gauge group being just SU(3)_C x SU(2)_L x U(1)_Y and the SU(3)_C x SU(2)_L x U(1)_Y-charged spectrum of the observable sector consisting solely of the MSSM spectrum. Associated with this model is a set of distinct flat directions of vacuum expectation values (VEVs) of non-Abelian singlet fields that all produce solely the MSSM spectrum. In this paper, we study the effective superpotential induced by these choices of flat directions. We investigate whether sufficient degrees of freedom exist in these singlet flat directions to satisfy various phenomenological constraints imposed by the observed Standard Model data. For each flat direction, the effective superpotential is given to sixth order. The variations in the singlet and hidden sector low energy spectrums are analyzed. We then determine the mass matrices (to all finite orders) for the three generations of MSSM quarks and leptons. Possible Higgs mu-terms are investigated. We conclude by considering generalizations of our flat directions involving VEVs of non-Abelian fields.Comment: 41 pages. Standard Late

Phenomenology of Non-Abelian Flat Directions in a Minimal Superstring Standard Model

Recently, we presented the first non-Abelian flat directions that produce from a heterotic string model solely the three-generation MSSM states as the massless spectrum in the observable sector of the low energy effective field theory. In this paper we continue to develop the systematic techniques for the analysis of nonrenormalizable superpotential terms and non-Abelian flat direction in realistic string models. Some of our non-Abelian directions were F-flat to all finite orders in the superpotential. We study for the same string model the varying phenomenologies resulting from a large set of such all-order flat directions. We focus on the quark, charged lepton, and Higgs doublet mass matrices resulting for our phenomenologically superior non-Abelian flat direction. We review and apply a string-related method for generating large mass hierarchies between MSSM generations, first discussed in string-derived flipped SU(5) models, when all generational mass terms are of renormalizable or very low non-renormalizable order

Interaction potentials for soft and hard ellipsoids

Using results from colloid science we derive interaction potentials for computer simulations of mixtures of soft or hard ellipsoids of arbitrary shape and size. Our results are in many respects reminicent of potentials of the Gay-Berne type but have a well-defined microscopic interpretation and no adjustable parameters. Since our potentials require the calculation of similar variables, the modification of existing simulation codes for Gay-Berne potentials is straightforward. The computational performance should remain unaffected.Comment: 8 pages, 4 figure

Computer simulations of hard pear-shaped particles

We report results obtained from Monte Carlo simulations investi- gating mesophase formation in two model systems of hard pear-shaped particles. The first model considered is a hard variant of the trun- cated Stone-Expansion model previously shown to form nematic and smectic mesophases when embedded within a 12-6 Gay-Berne-like po- tential [1]. When stripped of its attractive interactions, however, this system is found to lose its liquid crystalline phases. For particles of length to breadth ratio k = 3, glassy behaviour is seen at high pressures, whereas for k = 5 several bi-layer-like domains are seen, with high intradomain order but little interdomain orientational correlation. For the second model, which uses a parametric shape parameter based on the generalised Gay-Berne formalism, results are presented for particles with elongation k = 3; 4 and 5. Here, the systems with k = 3 and 4 fail to display orientationally ordered phases, but that with k = 5 shows isotropic, nematic and, unusually for a hard-particle model, interdigitated smectic A2 phases.</p

Non-equilibrium flow in plane expansion waves

The non-equilibrium supersonic flow of a relaxing or reacting gas through a plane expansion has been studied from a numerical,, analytical and experimental point of view. The flow of an ideal dissociating gas in a two dimensional expansion has been solved numerically by writing the governing equations of motion in their characteristic form. In conflict with linearised theory along the wall, the numerical solutions do not asymptote to the infinite rate equilibrium values. To estimate how far the asymptotic state deviates from the infinite rate equilibrium values, a formal second order solution has been developed with the aid of transform techniques. An example has been discussed for a simplified relaxing gas model, and estimates of the asymptotic state have been obtained. An exact solution over the whole field was not possible but by treating the parameter as small, an approximate answer has been found. To understand in more detail the coupling effects of two relaxation processes, linearised theory has been extended to cope with the flow of a gas with more than one relaxing mode. An example has been discussed far Carbon Dioxide and the effect of possible coupling between the bending and stretching modes of the molecule in a plane expansion has been investigated. The Mach-Zehnder interferometer and Schlieren method have been used in conjunction with a 2" - diameter shock tube to study the density and density gradients within, and following a sharp two-dimensional expansion for shock heated Carbon Dioxide. Measurement of the density gradient at the leading edge of the expansion by quantitative Schlieren methods have allowed relaxation times to be obtained. This method has the advantage that relaxation times can be obtained for specific values of the density and temperature for only small departures from an equilibrium state