Capillary-wave models and the effective average action scheme of functional renormalization group

We reexamine the functional renormalization-group theory of wetting transitions. As a starting point of the analysis we apply an exact equation describing renormalization group flow of the generating functional for irreducible vertex functions. We show how the standard nonlinear renormalization group theory of wetting transitions can be recovered by a very simple truncation of the exact flow equation. The derivation makes all the involved approximations transparent and demonstrates the applicability of the approach in any spatial dimension d\geq 2. Exploiting the non-uniqueness of the renormalization-group cutoff scheme, we find however, that the capillary parameter omega is a scheme-dependent quantity below d=3. For d=3 the parameter omega is perfectly robust against scheme variation.