A Measure of Cosmological Acceleration
  We propose quantifying the quantum gravitational back-reaction on inflation with an invariant measure of the local acceleration rather than the expansion rate. Our observable is suitable for models in which there is no scalar inflaton to provide a preferred velocity field with which to define the expansion. As an example, we use stochastic techniques to evaluate the local acceleration at one loop order for Lambda-driven inflation in pure quantum gravity. 
N. C. Tsamis (University of Crete) and R. P. Woodard (University of   Florida)