Renormalization group flow of f(R) gravity

We use the functional renormalization group equation for quantum gravity to construct a nonperturbative flow equation for modified gravity theories of the form S=integral d(d)x root gf(R). Based on this equation we show that certain gravitational interaction monomials can be consistently decoupled from the renormalization group (RG) flow and reproduce recent results on the asymptotic safety conjecture. The nonperturbative RG flow of nonlocal extensions of the Einstein-Hilbert truncation including integral d(d)x root gln(R) and integral d(d)x root gR(-n) interactions is investigated in detail. The inclusion of such interactions resolves the infrared singularities plaguing the RG trajectories with positive cosmological constant in previous truncations. In particular, in some R-n truncations all physical trajectories emanate from a non-Gaussian (UV) fixed point and are well-defined on all RG scales. The RG flow of the ln(R) truncation contains an infrared attractor which drives a positive cosmological constant to zero dynamically.