On the realization of assisted inflation

We consider conditions necessary for a successful implementation of the so-called assisted inflation. We generalize the applicability of assisted inflation beyond exponential potentials as originally proposed to include standard chaotic ($\lambda {\phi }^4$ or $m^2{\phi }^2$) models as well. We also demonstrate that in a purely four-dimensional theory, unless the assisted sector is in fact decoupled, the additional fields of the assisted sector actually impede 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 for a fine-tuned quartic coupling to drive chaotic inflation. This is a general result of models with one or more “large” extra dimensions.