Generating the primordial curvature perturbation from inflation

The scale–independence of the primordial curvature perturbation suggests that it comes from the vacuum fluctuation during inflation of a light scalar field. This field may be the inflaton, or a different `curvaton’ field. The observation of primordial non–gaussianity would be a smoking gun for the curvaton model, while the observation of gravitational waves originating during slow–roll inflation would rule out the model.