On natural inflation

We reexamine the model of natural inflation, in which the inflaton potential is flat due to shift symmetries. The original version of the model, where the inflaton is a pseudo–Nambu-Goldstone boson with potential of the form [Formula Presented], is studied in light of recent data. We find that the model is alive and well. Successful inflation as well as data from the Wilkinson Microwave Anisotropy Probe require [Formula Presented] (where [Formula Presented]) and [Formula Presented] (where [Formula Presented]), scales which can be accommodated in particle physics models. The detectability of tensor modes from natural inflation in upcoming microwave background experiments is discussed. We find that natural inflation predicts a [Formula Presented] ratio within reach of future observations.