We present a minimal axion inflation model which can generate a large tensor-to-scalar ratio while remaining sub-Planckian .
The modulus of a complex scalar field \Phi with a \lambda| \Phi| ^ { 4 } potential couples directly to the gauge field of a strongly-coupled sector via a term of the form ( | \Phi| / M _ { Pl } ) ^ { m } F \tilde { F } .
This generates a minimum of the potential which is aperiodic in the phase .
The resulting inflation model is equivalent to a \phi ^ { 4 / ( m + 1 ) } chaotic inflation model .
For the natural case of a leading-order portal-like interaction of the form \Phi ^ { \dagger } \Phi F \tilde { F } , the model is equivalent to a \phi ^ { 4 / 3 } chaotic inflation model and predicts a tensor-to-scalar ratio r = 16 / 3 N = 0.097 and a scalar spectral index n _ { s } = 1 - 5 / 3 N = 0.970 .
The value of | \Phi| remains sub-Planckian throughout the observable era of inflation , with | \Phi| ^ { < } _ { \sim } 0.01 M _ { Pl } for N \lesssim 60 when \lambda \sim 1 .