2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/194285A gauge invariant metric fluctuations formalism from a non-compact Kaluza-Klein (NKK) theory of gravity is presented in this talk notes. In this analysis we recover the well-known result $\frac{delta ρ}ρ\simeq 2Φ$ obtained typically in the standard 4D semiclassical approach to inflation and also the spectrum of this fluctuations becomes dependent of the fifth (space-like) coordinate. This fact allows to establish an interval of values for the wave number associated with the fifth dimension.Talk notes accepted for publication in the proceedings of the 6th Workshop on Gravitation and Mathematical Physics, Metepec, Mexico, 20-25 Nov. 2005General Relativity and Quantum CosmologyAstrophysicsHigh Energy Physics - Theorytext