Signatures of extra dimensions in gravitational waves
  Considering gravitational waves propagating on the most general
4+N-dimensional space-time, we investigate the effects due to the N extra
dimensions on the four-dimensional waves. All wave equations are derived in
general and discussed. On Minkowski4 times an arbitrary Ricci-flat compact
manifold, we find: a massless wave with an additional polarization, the
breathing mode, and extra waves with high frequencies fixed by Kaluza-Klein
masses. We discuss whether these two effects could be observed.
