Higher-curvature corrections and tensor modes

Higher-curvature corrections to the effective gravitational action may leave signatures in the spectrum of primordial tensor perturbations if the inflationary energy scale is sufficiently high. In this paper, we further investigate the effects of a coupling of the Inflaton field to higher-curvature tensors in models with a minimal breaking of conformal symmetry. We show that an observable violation of the tensor consistency relation from higher-curvature tensors implies also a relatively large running of the tensor tilt, enhanced even by some order of magnitude with respect to the standard slow-roll case. This may leave signatures in the tensor two-point function that we could test to recognize higher-curvature effects, above all if they are translated into a blue tilted spectrum visible by future gravitational wave experiments. Exploiting current cosmic microwave background and gravitational wave data, we also derive constraints on the inflationary parameters, inferring that large higher-curvature corrections seem to be disfavored.

Automated summary

This paper investigates the effects of higher-curvature corrections on the spectrum of primordial tensor perturbations. It shows that observable violation of the tensor consistency relation from higher-curvature tensors can lead to relatively large changes in tensor tilt. This may leave signatures in the tensor two-point function that can be tested to identify higher-curvature effects, especially if they result in a blue tilted spectrum visible in future gravitational wave experiments.