The recent conjecture of possible equivalence between the string scale MS and the minimal supersymmetric standard model unification scale MU ≈ 2.5× 1016 GeV is considered in the context of string… (More)

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… (More)

We investigate some issues relating to recently proposed fractional superstring theories with Dcritical < 10. Using the factorization approach of Gepner and Qiu, we systematically rederive the… (More)

The implications of string theory for understanding the dimension of uncompactified spacetime are investigated. Using recent ideas in string cosmology, a new model is proposed to explain why three… (More)

We derive expressions for the Ricci curvature tensor and scalar in terms of intrinsic torsion classes of half-flat manifolds by exploiting the relationship between half-flat manifolds and non-compact… (More)

We develop techniques to classify Dand F -flat directions for N = 1 supersymmetric string vacua of the perturbative heterotic string theory, which possess an anomalous U(1) gauge group at the tree… (More)

Consistent heterotic free fermionic string models are classified in terms of their number of spacetime supersymmetries, N. For each of the six distinct choices of gravitino sector, we determine what… (More)

The orbifold GUT doublet–triplet splitting mechanism was discussed in 1994 in the framework of the NAHE–based free fermionic models in which the SO(10) GUT symmetry is broken to SO(6) × SO(4), SU(3)… (More)

Recently it was demonstrated that free fermionic heterotic–strings can produce models with solely the Minimal Supersymmetric Standard Model states in the low energy spectrum. This unprecedented… (More)

Three family SU(3)C × SU(2)L ×U(1)Y string models in several constructions generically possess two features: (i) an extra local anomalous U(1)A and (ii) numerous (often fractionally charged) exotic… (More)