Distinguishing between Extra Natural Inflation and Natural Inflation   after BICEP2
  In this paper, we carefully calculated the tensor-to-scalar ratio, the running spectral index, and the running of running spectrum for (extra) natural inflation in order to compare with recent BICEP2 data, PLANCK satellite data and future 21 cm data. We discovered that the prediction for running spectral index and the running of running spectrum in natural inflation is different from that in the case of extra natural inflation. Near future observation for the running spectral index may achieve enough accuracy to allow us distinguishing between extra natural inflation from natural inflation. Distinguishing the models by using the running of running spectrum is not impossible but would be more challenging for future experiments. 
Kazunori Kohri, C. S. Lim, Chia-Min Lin
hep-ph astro-ph.CO hep-th