Cuscuton Inflation

TL;DR

This paper explores how generalized cuscuton models influence single scalar field inflation, showing they produce nearly scale-invariant spectra with potential for observable tensor-to-scalar ratios and distinctive bispectrum shapes, while remaining consistent with current non-Gaussianity constraints.

Contribution

It introduces the impact of generalized cuscuton models on inflation, highlighting their slow-roll suppressed modifications and potential for new observable signatures in the bispectrum shape.

Findings

Cuscuton models do not disrupt inflation and produce nearly scale-invariant spectra.

They allow a wider parameter space for observable quantities like tensor-to-scalar ratio.

Non-Gaussianities are suppressed but may have distinctive shapes detectable in future experiments.

Abstract

We study the impact of (generalized) cuscuton models on standard single scalar field inflation. Generalized cuscuton models are characterized by spatial covariant gravity where a scalar degree of freedom is made non dynamical, and there are just two tensor degrees of freedom. The presence of the non-dynamical scalar field does not spoil inflation but instead the modifications are, in general, slow-roll suppressed leading to almost scale-invariant power spectra. However, the extra free parameters, which can be tuned relatively independently, lead to a larger parameter range for observable quantities, such as the tensor-to-scalar ratio. For the (generalized) cuscuton model the non-Gaussianties of the curvature bispectrum are suppressed by the slow-roll parameters, and, therefore, outside the reach of current experiments. However, generalized cuscuton models can lead to a different shape for the bispectrum which might be constrained by future experiments.