Hamilton-Jacobi formalism for inflation with non-minimal derivative coupling

TL;DR

This paper introduces a Hamilton-Jacobi approach to analyze inflation models with non-minimal derivative coupling, simplifying calculations and enabling comparison with observational data.

Contribution

It develops a Hamilton-Jacobi formalism for non-minimal derivative coupling inflation models, bypassing complex conformal transformations and perturbation calculations.

Findings

Models are consistent with Planck data

Tensor-to-scalar ratio matches observations

Spectral index and running agree with measurements

Abstract

In inflation with nonminimal derivative coupling there is not a conformal transformation to the Einstein frame where calculations are straightforward, and thus in order to extract inflationary observables one needs to perform a detailed and lengthy perturbation investigation. In this work we bypass this problem by performing a Hamilton-Jacobi analysis, namely rewriting the cosmological equations considering the scalar field to be the time variable. We apply the method to two specific models, namely the power-law and the exponential cases, and for each model we calculate various observables such as the tensor-to-scalar ratio, and the spectral index and its running. We compare them with 2013 and 2015 Planck data, and we show that they are in a very good agreement with observations.