Precision predictions for the primordial power spectra from f(R) models of inflation

We study the power spectra of f(R) inflation using a new technique in which the norm-squared of the mode functions is evolved. Our technique results in excellent analytic approximations for how the spectra depend upon the function f(R). Although the spectra are numerically the same in the Jordan and Einstein frames for the same wave number k, they depend upon the geometries of these frames in quite different ways. For example, the power spectra in the two frames are different functions of the number of e-foldings until end of inflation. We discuss how future data on reheating can be used to distinguish f(R) inflation from scalar-driven inflation.