Primordial non-Gaussianity from G inflation

Abstract

We present a comprehensive study of primordial fluctuations generated from G inflation, in which the inflaton Lagrangian is of the form K(ϕ,X)-G(ϕ,X)□ϕ with X=-(∂ϕ)[2]/2. The Lagrangian still gives rise to second-order gravitational and scalar field equations, and thus offers a more generic class of single-field inflation than ever studied, with a richer phenomenology. We compute the power spectrum and the bispectrum, and clarify how the non-Gaussian amplitude depends upon parameters such as the sound speed. In so doing we try to keep as great generality as possible, allowing for non slow-roll and deviation from the exact scale invariance.