Consequences of U dualities for intersecting branes in the Universe

We consider N-charge, intersecting brane-antibrane configurations in M theory which are smeared uniformly in the common transverse space and may describe our universe. We study the consequences of U dualities and find that they imply relations among the scale factors. We find using Einstein's equations that U dualities also imply a relation among the density ρ and the pressure pi for the single charge case. We present an ansatz for ρ and pi for the N-charge case which yields all the U duality relations among the scale factors. We then study configurations with identical charges, and also with net charges vanishing. We find among other things that, independent of the details of the brane-antibrane dynamics, such four charge configurations lead asymptotically to an effective (3+1)-dimensional expanding universe.