Parameter Space Investigations of Free Fermionic Heterotic Models

I survey the parameter space of NAHE-based free fermionic heterotic string models. First, I discuss flat directions of the low energy effective field theories and show that D-flat directions need not be isomorphic to gauge invariant superpotential terms. Next, I review recent studies of three generation SU(3)_C x SU(2)_L x U(1)_Y, SU(3)_C x SU(2)_L x SU(2)_R x U(1)_B-L, SU(4)_C x SU(2)_L x U(1)_Y', and flipped SU(5) models, constructed by Wilson breaking of the underlying SO(10) observable sector gauge group of the NAHE Z_2 x Z_2 basis. Based on talk presented at the First International Conference on String Phenomenology.Comment: 9 pages. Standard Late

Phenomenological Survey of a Minimal Superstring Standard Model

We discuss a heterotic-string solution 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 fields that all produce solely the MSSM spectrum. Some of these directions only involve VEVs of non-Abelian singlet fields while others also contain VEVs of non-Abelian charged fields.Comment: 5 pages. Latex w/ sprocl.sty. Talk presented at PASCOS 9

In Search of the (Minimal Supersymmetric) Standard Model String

This paper summarizes several developments in string-derived (Minimal Supersymmetric) Standard Models. Part one reviews the first string model containing solely the three generations of the Minimal Supersymmetric Standard Model and a single pair of Higgs as the matter in the observable sector of the low energy effective field theory. This model was constructed by Cleaver, Faraggi, and Nanopoulos in the Z_2 x Z_2 free fermionic formulation of weak coupled heterotic strings. Part two examines a representative collection of string/brane-derived MSSMs that followed. These additional models were obtained from various construction methods, including weak coupled Z_6 heterotic orbifolds, strong coupled heterotic on elliptically fibered Calabi-Yau's, Type IIB orientifolds with magnetic charged branes, and Type IIA orientifolds with intersecting branes (duals of the Type IIB). Phenomenology of the models is compared. To appear in String Theory Research Progress, Ferenc N. Balogh, editor., (ISBN 978-1-60456-075-6), Nova Science Publishers, Inc.}Comment: 57 pages, latex, typos removed, references added. To appear as Chapter 2 in in String Theory Research Progress, Ferenc N. Balogh, editor., (ISBN 978-1-60456-075-6), Nova Science Publishers, In

Quark Masses and Flat Directions in String Models

I discuss a method for producing a quasi-realistic inter-generational quark mass hierarchy in string models. This approach involves non-Abelian singlet states developing intermediate scale vacuum expectation values. I summarize recent investigations into string model realization of this. Talk presented at QCD98, Paris, France, 1-6 June 1998.Comment: 10 pages. Standard Late

GUT's with Adjoint Higgs from Superstrings

I discuss how effective grand unified theories requiring adjoint Higgs fields for breaking to the standard model can be contained within string theory. Initial findings are presented in a search for and classification of effective three generation SO(10) SUSY-GUT models built using the free-fermionic string approach. Based on talk presented at PASCOS '94, Syracuse, NY.Comment: 11 pages OHSTPY-HEP-T-94-007. Some clarification of statements. Correction to references. Use standard TeX. One table not included. To receive table please send request to [email protected]

What's New in Stringy SO(10) SUSY-GUTS

Report in extended abstract form. Based on talk given at Strings '95, Los Angeles, CA. This is a summary of the findings initially presented in hep-th/9505080. Results of a step (the complete classification of free fermionic solutions to $N=1$ spacetime) in the search for stringy three-generation SO(10) SUSY-GUTs are reviewed.Comment: 3 pages, jytex; hep-th # chang

The Dimension of Decompactified Spacetime from String Theory

The implications of string theory for understanding the dimension of decompactified spacetime are discussed. Results from a computer model designed to simulate expansion of the early universe during the string dominated phase are presented. This model focuses on the effects of string winding modes on inflation and is based on the theory of random walks. We demonstrate that our decompactified four-dimensional spacetime can be explained by the proper choice of initial conditions.Comment: 12 pages, OHSTPY-HEP-T-94-006, A condensed version of HEP-TH/9402088 to appear in the Proceedings of Supersymmetry 1994, Ann Arbor, Michigan, May, 1994. Use standard TeX. Seven figures not included. To receive figures please send request to [email protected]

Warp Drive: A New Approach

Certain classes of higher dimensional models suggest that the Casimir Effect is a candidate for the cosmological constant. In this paper we demonstrate that a sufficiently advanced civilization could, in principal, manipulate the radius of the extra dimension to locally adjust the value of the cosmological constant. This adjustment could be tuned to generate an expansion/contraction of spacetime around a spacecraft creating an exotic form of field-propulsion. Due to the fact that spacetime expansion itself is not restricted by relativity, a faster-than-light 'warp drive' could be created. Calculations of the energy requirements of such a drive are performed and an 'ultimate' speed limit, based on the Planckian limits on the size of the extra dimensions is found.Comment: 15 pages. To be published in JBI

Hawking Radiation as a Probe for the Interior Structure of Regular Black Holes

The notion of the black hole singularity and the proof of the singularity theorem were considered great successes in classical general relativity. Singularities had presented deep puzzles to physicists. Conceptual challenges were set up by the intractability of the singularity. The existence of black hole horizons which cover up the interior, including the singularity of the black hole from outside observers, builds an information curtain, further hindering physicists from understanding the nature of the singularity and the interior structure of black holes. The regular black hole is a concept produced out of multiple attempts of establishing a tractable and understandable interior structure for black hole as well as avoiding the singularity behind the black hole horizon. A method is needed to check the correctness of the new constructions of black holes. After studying the Hawking radiation by fermion tunnelling from one type of regular black hole, structure dependent results were obtained. The result being structure dependent points out the prospects of employing the Hawking radiation as a method to probe into the structure of black holes

Randall-Sundrum and Flipped SU(5)

In this letter, we construct a model based on a flipped SU(5) partial grand unified theory, within the framework of the Randall-Sundrum (RS1) proposal. Breaking of $\widetilde{SU}(5)$ is achieved using a bulk scalar field in the \textbf{10} of SU(5), $\Phi$, which gains a vacuum expectation value $\left< \Phi\right> \sim 3 \times 10^{15}$ GeV. We are able to retain the successes of the flipped SU(5) phenomenology, namely the elimination of the doublet-triplet splitting problem and the confinement of all fields to the smallest (\textbf{1}, $\mathbf{\bar{5}}$, and \textbf{10}) representations of SU(5). We derive the beta functions, and point out some constraints on bulk matter content implied by the runnings (and positivity) of the five dimensional coupling. Finally, we comment on baryon decay and show the fine-tuning problem required to prevent an exponentially short proton lifetime.Comment: 21 pages and 3 (eps) figs. Typos corrected, refs adde