Higher Dimensional Cosmology: Relations among the radii of two
  homogeneous spaces
  We study a cosmological model in 1+D+d dimensions where D dimensions are
associated with the usual Friedman-Robertson-Walker type metric with radio a(t)
and d dimensions corresponds to an additional homogeneous space with radio
b(t). We make a general analysis of the field equations and then we obtain
solutions involving the two cosmological radii, a(t) and b(t). The particular
case D=3, d=1 is studied in some detail.
