Gauge invariant backreaction in general single field models of inflation

In a general single field inflationary model, we consider the effects of long wavelength scalar fluctuations on the effective expansion rate and equation of state seen by a class of free-falling observers, using a physical gauge invariant formulation. In a previous work we showed that for a free massive inflaton no backreaction is observed within some constraints. In this paper we extend the validity of our previous results to the case of an arbitrary self-interacting inflation potential, working to second order in cosmological perturbation theory and to all order in slow-roll approximation. For these general inflationary models, we also show the equivalence of the free-falling observers to the ones comoving with the inflaton field.