The lessons from the running of the tensor-to-scalar ratio

TL;DR

This paper derives a new consistency relation involving the running of the tensor-to-scalar ratio in inflationary models, which can distinguish between single and multi-field scenarios and may be tested by future laser interferometer experiments.

Contribution

It introduces a simple, first-order consistency relation for the running of the tensor-to-scalar ratio that captures multi-field effects and can be observationally tested.

Findings

Multi-field models show non-trivial contributions dependent on field space geometry.

The running of the tensor-to-scalar ratio can be used to probe inflationary dynamics.

Potential detection by future laser interferometer experiments.

Abstract

We derive a simple consistency relation from the running of the tensor-to-scalar ratio. This new relation is first order in the slow-roll approximation. While for single field models we can obtain what can be found by using other observables, multi-field cases in general give non-trivial contributions dependent on the geometry of the field space and the inflationary dynamics, which can be probed observationally from this relation. The running of the tensor-to-scalar ratio may be detected by direct laser interferometer experiments.