Producing primordial fluctuations with quadratic curvature terms

We study cosmological perturbations in an effective theory of gravity described by a linear combination of the scalar curvature R, R², and the Weyl tensor squared. Higher-order time derivatives induced by the Weyl-squared term are treated self-consistently by applying reduction of order, so only physically relevant solutions are considered. Deviations from the predictions of Starobinsky inflation to the tensor and scalar primordial power spectra are also discussed.