On the constant-roll inflation
  The primordial power spectra of scalar and tensor perturbations during
slow-roll inflation are usually calculated with the method of Bessel function
approximation. For constant-roll or ultra slow-roll inflation, the method of
Bessel function approximation may be invalid. We compare the numerical results
with the analytical results derived from the Bessel function approximation, and
we find that they differ significantly on super-horizon scales if the constant
slow-roll parameter $\eta_H$ is not small. More accurate method is needed for
calculating the primordial power spectrum for constant-roll inflation.
