The BICEP2 observation of a large tensor-to-scalar ratio , r = 0.20 ^ { +0.07 } _ { -0.05 } , implies that the inflaton \phi in single-field inflation models must satisfy \phi \sim 10 M _ { Pl } in order to produce sufficient inflation .
This is a problem if interaction terms suppressed by the Planck scale impose a bound \phi ^ { < } _ { \sim } M _ { Pl } .
Here we consider whether it is possible to have successful sub-Planckian inflation in the case of two-field inflation .
The trajectory in field space can not be radial if the effective single-field inflaton is to satisfy the Lyth bound .
By considering a complex field \Phi , we show that a near circular but aperiodic modulation of a | \Phi| ^ { 4 } potential can reproduce the results of \phi ^ { 2 } chaotic inflation for n _ { s } and r while satisfying | \Phi| ^ { < } _ { \sim } 0.01 M _ { Pl } throughout .
More generally , for models based on a | \Phi| ^ { 4 } potential , the simplest sub-Planckian models are equivalent to \phi ^ { 2 } and \phi ^ { 4 / 3 } chaotic inflation .