Mimetic Inflation

TL;DR

This paper explores a ghost-free extension of mimetic gravity with higher derivative interactions, revealing novel inflationary properties, modified perturbation relations, and potential observable non-Gaussianities.

Contribution

It introduces a higher derivative mimetic gravity model that remains stable and exhibits unique inflationary features, including modified dispersion relations and non-Gaussianities.

Findings

Scalar perturbations have quartic momentum corrections.

Tensor tilt can be positive or negative with a modified consistency relation.

Non-Gaussianities in various shapes are generated with observable amplitudes.

Abstract

We study inflationary solution in an extension of mimetic gravity with the higher derivative interactions coupled to gravity. Because of the higher derivative interactions, the setup is free from the ghost and gradient instabilities while it hosts a number of novel properties. The dispersion relation of scalar perturbations develops quartic momentum correction similar to the setup of ghost inflation. Furthermore, the tilt of tensor perturbations can take either signs with a modified consistency relation between the tilt and the amplitude of tensor perturbations. Despite the presence of higher derivative interactions coupled to gravity, the tensor perturbations propagate with a speed equal to the speed of light as required by the LIGO observations. Furthermore, the higher derivative interactions induce non-trivial interactions in cubic Hamiltonian, generating non-Gaussianities in various shapes such as the equilateral, orthogonal, and squeezed configurations with observable amplitudes.