Semiclassical analysis of the tensor power spectrum in the Starobinsky inflationary model

In this work we calculate the tensor power spectrum and the tensor-to-scalar ratio r within the frame of the Starobinsky inflationary model using the improved uniform approximation method and the third-order phase-integral method. We compare our results with those obtained with numerical integration and the slow-roll approximation to second order. We have obtained consistent values of r using the different approximations, and r is inside the interval reported by observations.