Non-renormalizable terms and M theory during inflation

Inflation is well known to be difficult in the context of supergravity, if the potential is dominated by the F term. Non-renormalizable terms generically give |V′′|∼V/M2, where V(φ) is the inflaton potential and M is the scale above which the effective field theory under consideration is supposed to break down. This is equivalent to |η|∼(MPl/M)2>1 where MPl=(8πG)−1/2, but inflation requires |η|<0.1. I here point out that all of the above applies also if the D term dominates, with the crucial difference that the generic result is now easily avoided by imposing a discrete symmetry. I also point out that if extra spacetime dimensions appear well below the Planck scale, as in a recent M-theory model, one expects M≪MPl, which makes the problem worse than if M∼MPl.