Constraints in the Context of Induced-gravity Inflation

Constraints on the required flatness of the scalar potential $V(\varphi )$ for a cousin-model to extended inflation are studied. It is shown that, unlike earlier results, Induced-gravity Inflation can lead to successful inflation with a very simple lagrangian and $\lambda \sim {10}^{-6}$, rather than ${10}^{-15}$ as previously reported. A second order phase transition further enables this model to escape the \lq big bubble’ problem of extended inflation, while retaining the latter’s motivations based on the low-energy effective lagrangians of supergravity, superstring, and Kaluza-Klein theories.