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.
