We study the restrictions imposed by cancellation of the tadpoles for two, three, and four-form gauge fields in string theory, M-theory and F-theory compactified to two, three and four dimensions,â€¦ (More)

We study the properties of M and F theory compactifications to three and four dimensions with background fluxes. We provide a simple construction of supersymmetric vacua, including some withâ€¦ (More)

Supersymmetry is used to derive conditions on higher derivative terms in the effective action of type IIB supergravity. Using these conditions, we are able to prove earlier conjectures that certainâ€¦ (More)

We show that three-dimensional N=8 Sp(N) and SO(2N + 1) gauge theories flow to the same strong coupling fixed point. As a consequence, the corresponding orientifold two-planes in type IIA stringâ€¦ (More)

The light-like linear dilaton background represents a particularly simple timedependent 1/2 BPS solution of critical type IIA superstring theory in ten dimensions. Its lift to M-theory, as well asâ€¦ (More)

We modify and extend an earlier proposal by Brown and Teitelboim to relax the effective cosmological term by nucleation of branes coupled to a three-index gauge potential. Microscopic considerationsâ€¦ (More)

We study string compactifications with sixteen supersymmetries. The moduli space for these compactifications becomes quite intricate in lower dimensions, partly because there are many differentâ€¦ (More)

We consider supersymmetric gauge theories with impurities in various dimensions. These systems arise in the study of intersecting branes. Unlike conventional gauge theories, the Higgs branch of anâ€¦ (More)

We study the dynamics of D-branes in a smooth time-dependent background. The theory on the branes is a time-dependent noncommutative field theory. We find the metric and fluxes that determine theâ€¦ (More)

The matrix model formulation of M-theory can be generalized by compactification to ten-dimensional type II string theory, formulated in the infinite momentum frame. Both the type IIA and IIB stringâ€¦ (More)