Observable Gravitational Waves and Spectral Index Running in Small Single Field Inflationary Models

I construct a class of single small field models of inflation that can predict an observable gravitational wave signal in the cosmic microwave background anisotropies, contrary to popular wisdom. The spectral index, its running, the tensor to scalar ratio and the number of e-folds can cover all the parameter space currently allowed by cosmological observations. A unique feature of models in this class is their ability to predict a negative spectral index running in accordance with recent cosmic microwave background observations. I comment on the new class of models from an effective field theory perspective and show that if the dimensionless trilinear coupling is small, as required for consistency, then the observed spectral index running implies a high scale of inflation and hence an observable gravitational wave signal.