We investigate preheating in a higher-dimensional generalized Kaluza-Klein
theory with a quadratic inflaton potential V(Ο)=21βm2Ο2
including metric perturbations explicitly. The system we consider is the
multi-field model where there exists a dilaton field Ο which corresponds
to the scale of compactifications and another scalar field Ο coupled to
inflaton with the interaction 21βg2Ο2Ο2+g~β2Ο3Ο.
In the case of g~β=0, we find that the perturbation of dilaton does not
undergo parametric amplification while the Ο field fluctuation can be
enhanced in the usual manner by parametric resonance. In the presence of the
g~β2Ο3Ο coupling, the dilaton fluctuation in sub-Hubble scales
is modestly amplified by the growth of metric perturbations for the large
coupling g~β. In super-Hubble scales, the enhancement of the dilaton
fluctuation as well as metric perturbations is weak, taking into account the
backreaction effect of created Ο particles. We argue that not only is it
possible to predict the ordinary inflationary spectrum in large scales but
extra dimensions can be held static during preheating in our scenario.Comment: 21 pages, 7 figures, submitted to JHE