We discuss a supersymmetric version of DBI ( Dirac-Born-Infeld ) inflation , which is a typical inflation model in string cosmology .
The supersymmetric DBI action together with a superpotential always leads to correction terms associated with the potential into the kinetic term , which drastically change the dynamics of DBI inflation .
We find two significant features of supersymmetric DBI inflation .
The first one is that ultra-relativistic motion is prohibited to cause inflation , which leads to order of unity sound velocity squared and hence small non-Gaussianities of primordial curvature perturbations .
The second one is that the relation between the tensor-to-scalar ratio and the field variation is modified .
Then , significant tensor-to-scalar ratio r \gtrsim 0.01 is possible because the variation of the canonically normalized inflaton can be beyond the reduced Planck scale .
These new features are in sharp contrast with those of the standard non-supersymmetric DBI inflation and hence have a lot of interest implications on upcoming observations of cosmic microwave background ( CMB ) anisotropies by the Planck satellite as well as direct detection experiments of gravitational waves like DECIGO and BBO .