Observational signatures and non-Gaussianities of general single-field inflation

We perform a general study of primordial scalar non-Gaussianities in single-field inflationary models in Einstein gravity. We consider models where the inflaton Lagrangian is an arbitrary function of the scalar field and its first derivative, and the sound speed is arbitrary. We find that under reasonable assumptions, the non-Gaussianity is completely determined by five parameters. In special limits of the parameter space, one finds distinctive ‘shapes’ of the non-Gaussianity. In models with a small sound speed, several of these shapes would become potentially observable in the near future. Different limits of our formulae recover various previously known results.