2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/190049Recent fits of cosmological parameters by the Wilkinson Microwave Anisotropy Probe (WMAP) measurement favor a primordial scalar spectrum with varying index. This result, if stands, could severely constrain inflation model buildings. Most extant slow-roll inflation models allow for only a tiny amount of scale variations in the spectrum. We propose in this paper an extra-dimensional inflation model which is natural theoretically and can generate the required variations of the spectral index as implied by the WMAP for suitable choices of parameters.5 pages, 3 figures, REVTeX 4. Comments on low CMB quadrupoles added; Version accepted for publication in Phys. Rev. DAstrophysicsHigh Energy Physics - Phenomenologytext