Gauge-invariant metric fluctuations from NKK theory of gravity: de   Sitter expansion
  In this paper we study gauge-invariant metric fluctuations from a Noncompact Kaluza-Klein (NKK) theory of gravity in a de Sitter expansion. We recover the well known result $\delta\rho/\rho \simeq 2\Phi$, obtained from the standard 4D semiclassical approach to inflation. The spectrum for these fluctuations should be dependent of the fifth (spatial-like) coordinate. 
Jose Edgar Madriz Aguilar (IFM, UMSNH), Mariano Anabitarte, Mauricio   Bellini (Mar del Plata University & CONICET)