G-inflation: inflation driven by the Galileon field

TL;DR

G-inflation introduces a novel inflationary model with Galileon-like interactions, allowing for scale-invariant fluctuations, larger tensor-to-scalar ratios, and potential blue spectra, thus offering new observational prospects.

Contribution

It presents a new class of inflation models with second-order equations of motion and unique predictions for gravitational waves, expanding the landscape of inflationary theories.

Findings

Scale-invariant curvature fluctuations in de Sitter background

Enhanced tensor-to-scalar ratio exceeding standard models

Possibility of blue tensor spectral index

Abstract

We propose a new class of inflation model, G-inflation, which has a Galileon-like nonlinear derivative interaction of the form $G(\phi, (\nabla\phi)^2)\Box\phi$ in the Lagrangian with the resultant equations of motion being of second order. It is shown that (almost) scale-invariant curvature fluctuations can be generated even in the exactly de Sitter background and that the tensor-to-scalar ratio can take a significantly larger value than in the standard inflation models, violating the standard consistency relation. Furthermore, violation of the null energy condition can occur without any instabilities. As a result, the spectral index of tensor modes can be blue, which makes it easier to observe quantum gravitational waves from inflation by the planned gravitational-wave experiments such as LISA and DECIGO as well as by the upcoming CMB experiments such as Planck and CMBpol.