The parameter space for tree-level hybrid inflation

In a large region of parameter space, the tree-level hybrid inflation model is likely to be be invalidated by loop corrections. In particular, this is likely to be the case if both quartic couplings are of order unity, as is often supposed. It is likely also to be the case if there is an ultra-violet cutoff far below the Planck scale, ($\luv\lsim 10^9\GeV(V_0^{1/4}/1\MeV)^{2/5}$, where $V_0$ is the height of the potential) unless one allows field values bigger than the cutoff.