Strings, fivebranes and an expanding universe

It was recently shown that velocity-dependent forces between parallel fundamental strings moving apart in a D-dimensional spacetime implied an accelerating expanding universe in (D−1)-dimensional spacetime. Exact solutions were obtained for the early time expansion in D=5,6. Here we show that this result also holds for fundamental strings in the background of a fivebrane, and argue that the feature of an accelerating universe would hold for more general p-brane-seeded models.