One-loop modified gravity in a de Sitter universe, quantum-corrected inflation, and its confrontation with the Planck result

Motivated by issues on inflation, a generalized modified gravity model is investigated, where the model Lagrangian is described by a smooth function f(R, K, phi) of the Ricci scalar R, the kinetic term K of a scalar field phi. In particular, the one-loop effective action in the de Sitter background is examined on shell as well as off shell in the Landau gauge. In addition, the on-shell quantum equivalence of f(R) gravity in the Jordan and Einstein frames is explicitly demonstrated. Furthermore, we present applications related to the stability of the de Sitter solutions and the one-loop quantum correction to inflation in quantum-corrected R-2 gravity. It is shown that, for a certain range of parameters, the spectral index of the curvature perturbations can be consistent with the Planck analysis, but the tensor-to-scalar ratio is smaller than the minimum value within the 1 sigma error range of the BICEP2 result.