  It is demonstrated by explicit solutions of the (4+n)-dimensional vacuum
Einstein equations that accelerating cosmologies in the Einstein conformal
frame can be obtained by a time-dependent compactification of string/M-theory,
even in the case that internal dimensions are Ricci-flat, provided one includes
one or more geometric twists. Such acceleration is transient. When both compact
hyperbolic internal spaces and geometric twists are included, however, the
period of accelerated expansion may be made arbitrarily large.
