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

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.

Comments: (v1) 7 pages, 1 figure; (v2) Discussions refined and references added; (v3) More discussions on detectability, to appear in Physical Review D