Gauge Coupling Constant Unification With Planck Scale Values Of Moduli

Convergence of the standard model gauge coupling constants to a common value at around $2\times 10^{16}$ GeV is studied in the context of orbifold theories where the modular symmetry groups for $T$ and $U$ moduli are broken to subgroups of $PSL(2, Z)$. The values of the moduli required for this unification of coupling constants are studied for this case and also for the case where string unification is accompanied by unification to a gauge group larger then $SU(3)\times SU(2)\times U(1).$Comment: Tex, 15 pages, minor typos corrected and some references adde

CP-violating phases in the CKM matrix in orbifold compactifications

The picture of CP-violation in orbifold compactifications in which the $T$-modulus is at a complex fixed point of the modular group is studied. CP-violation in the neutral kaon system and in the neutron electric dipole moment are both discussed. The situation where the $T$-modulus takes complex values on the unit circle which are not at a fixed point is also discussed.Comment: LaTeX file 17 page

Modular Symmetries of Threshold Corrections for Abelian Orbifolds with Discrete Wilson Lines

The modular symmetries of string loop threshold corrections for gauge coupling constants are studied in the presence of discrete Wilson lines for all examples of abelian orbifolds, where the point group is realised by the action of Coxeter elements or generalised Coxeter elements on the root lattices of the Lie groups.Comment: 36 pages, Late

Dark Matter Constraints in Heterotic M-Theory with Five-Brane Dominance

The phenomenological implications of the M-theory limit in which supersymmetry is broken by the auxiliary fields of five-brane moduli is investigated. Assuming that the lightest neutralino provides the dark matter in the universe, constraints on the sparticle spectrum are obtained. Direct detection rates for dark matter are estimated.Comment: 10 pages, LaTeX file plus 8 EPS figure

Duality Symmetries in Orbifold Models

We derive the duality symmetries relevant to moduli dependent gauge coupling constant threshold corrections, in Coxeter ${\bf Z_N}$ orbifolds. We consider those orbifolds for which the point group leaves fixed a 2-dimensional sublattice $\Lambda_2$, of the six dimensional torus lattice $\Lambda_6$, where $\Lambda_6$ cannot be decomposed as $\Lambda_2 \bigoplus{\Lambda_4}.$Comment: 13 pages, QMW--TH--93/21, SUSX--TH--93/1

Background Symmetries In Orbifolds With Discrete Wilson Lines

Target space symmetries are studied for orbifold compactified string theories containing Wilson line background fields. The symmetries determined are for those moduli which contribute to the string loop threshold corrections of the gauge coupling constants. The groups found are subgroups of the modular group $PSL(2, Z)$ and depend on the choice of discrete Wilson lines and the shape of the underlying six-dimensional lattice.Comment: 31 pages, QMW--TH--94/0

Anisotropic Solutions For Orbifold Moduli From Duality Invariant Gaugino Condensates

The values of the $T$ and $U$ moduli are studied for those ${\bf Z}_N$ Coxeter orbifolds with the property that some of the twisted sectors have fixed planes for which the six-torus ${\bf T}^6$ can not be decomposed into a direct sum ${\bf T}^2\bigoplus {\bf T}^4$ with the fixed plane lying in ${\bf T}^2$. Such moduli in general transform under a subgroup of the modular group $SL(2,Z).$ The moduli are determined by minimizing the effective potential derived from a duality invariant gaugino condensate.Comment: QMW--TH--94/11, SUSX--TH--94/11, 16 page