A study of accelerating cosmologies from superstring/M theories

We study aspects of the accelerating cosmologies obtained from the compactification of the vacuum solution and S2-branes of superstring/M theories. The parameter dependence of the resulting expansion of our universe and internal space is examined for all cases. We find that accelerated expansions are obtained also from spherical internal spaces, albeit the solution enters a contracting phase eventually. The relation between the models of SM2- and SD2-branes is also discussed, and a potential problem with the SD2-brane model is noted.