Perspective on completing natural inflation
  We present a perspective on the inflation paths in 2-, 3-,,, N-flation models based on the ultraviolet completion in heterotic string theory, where a number of grand unification scale axions are used. The number of non-Abelian gauge groups for a natural inflation is restricted in string compactification, and we argue that the most plausible completion of natural inflation from a theory perspective is the 2-flation. 
Ki-Young Choi, Jihn E. Kim, Bumseok Kyae
hep-th astro-ph.CO hep-ph