Abstract
Imposing that the excursion distance of the inflaton in field space during inflation be less than the Planck scale, we derive an upper bound on the tensor-to-scalar ratio at the cosmic microwave background scales, i.e., , in the general canonical single-field slow-roll inflation model, in particular, the model with non-negligible running of the spectral index and/or the running of running . We find that for without running and running of running, and is significantly relaxed to the order of in the inflation model with and/or which are marginally preferred by the Planck 2015 data.
- Received 19 March 2015
DOI:https://doi.org/10.1103/PhysRevD.91.123532
© 2015 American Physical Society