On the realization of assisted inflation - art. no. 043502

We consider conditions necessary for a successful implementation of the so- called assisted inflation. We generalize the applicability of assisted infl ation beyond exponential potentials as originally proposed to include stand ard chaotic (lambda phi(4) or m(2)phi(2)) models as well. We also demonstra te that in a purely four-dimensional theory, unless the assisted sector is in fact decoupled, the additional fields of the assisted sector actually im pede inflation. As a specific example of an assisted sector, we consider a five-dimensional Kaluza-Klein (KK) model for which the extra dimension may be somewhat or much larger than the inverse Planck scale. In this case, the assisted sector (coming from a KK compactification) eliminates the need fo r a fine-tuned quartic coupling to drive chaotic inflation. This is a gener al result of models with one or more "large" extra dimensions. [S0556-2821( 99)05014-6].