Cuscuton inflation

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.

Automated summary

In this study, we investigate the impact of (generalized) cuscuton models on standard single scalar field inflation and find that the presence of a non-dynamical scalar field does not spoil inflation but instead leads to modifications that are slow-roll suppressed, resulting in almost scale invariant power spectra. However, the additional free parameters in this model can be tuned independently, allowing for a larger range of observable quantities.