We employ an algebraic approach for unifying perturbative and non-perturbative superstring states on an equal footing, in the form of U-duality multiplets, at all excited string levels. In compactiâ€¦ (More)

We extend Seibergâ€™s qualitative picture of the behavior of supersymmetric QCD to nonsupersymmetric models by adding soft supersymmetry breaking terms. In this way, we recover the standard vacuum ofâ€¦ (More)

The critical dimension of string theories in which the background metric is a product of Minkowski space and an SU(N) or O(N) group manifold is derived. A consistent string theory can be constructedâ€¦ (More)