We re-examine the original model of Natural inflation, in which the inflaton is a pseudo Nambu-Goldstone boson with potential of the form $ V(\phi) = \Lambda^4 [1 \pm \cos(\phi/f)]$, in light of recent data. We find that the model is alive and well. Successful inflation as well as recent data from the Wilkinson Microwave Anisotropy probe require $f > 0.6 m_{ \rm Pl}$ (where $m_{ \rm Pl} = 1.22 \times 10^{ 19}$ GeV) and $\Lambda \sim m_{ GUT}$, 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 tensor/scalar ratio within reach of future observations.
Categories: hep-ph astro-ph hep-th