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.
