Abstract
We investigate in detail the spectrum of gravitational waves induced by a peaked primordial curvature power spectrum generated in single-field inflationary models. We argue that the fNL parameter can be inferred by measuring the high frequency spectral tilt of the induced gravitational waves. We also show that the intrinsically non-Gaussian impact of fNL in ΩGW is to broaden its peak, although at a negligible level in order not to overproduce primordial black holes. We discuss possible degeneracies in the high frequency spectral tilt between fNL and a general equation of state of the universe w. Finally, we discuss the constraints on the amplitude, peak and slope (or equivalently, fNL) of the primordial power spectrum by combining current and future gravitational wave experiments with limits on μ distortions from the cosmic microwave background.