Preheating with extra dimensions

We investigate preheating in a higher-dimensional generalized Kaluza-Klein theory with a quadratic inflaton potential V (phi) = 1/2m(2)phi (2) including metric perturbations explicitly. The system we consider is the multi-field model where there exists a dilaton field sigma which corresponds to the scale of compactifications and another scalar field chi coupled to inflaton with the interaction 1/2g(2)phi (2)chi (2) + (g) over tilde (2)phi (3)chi. In the case of (g) over tilde = 0, we find that the perturbation of dilaton does not undergo parametric amplification while the chi field fluctuation can be enhanced in the usual manner by parametric resonance. In the presence of the (g) over tilde (2)phi (3)chi coupling, the dilaton fluctuation in sub-Hubble scales is modestly amplified by the growth of metric perturbations for the large coupling (g) over tilde. 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 chi 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.