Improved limits on the tensor-to-scalar ratio using BICEP and Planck data

We present constraints on the tensor-to-scalar ratio r using a combination of BICEP/Keck 2018 (BK18) and Planck PR4 data allowing us to fit for r consistently with the six parameters of the ??CDM model. We discuss the sensitivity of constraints on r to uncertainties in the ??CDM parameters as defined by the Planck data. In particular, we are able to derive a constraint on the reionization optical depth ?? and thus propagate its uncertainty into the posterior distribution for r. While Planck sensitivity to r is slightly lower than the current ground-based measurements, the combination of Planck with BK18 and baryon-acoustic-oscillation data yields results consistent with r = 0 and tightens the constraint to r < 0.032 at 95% confidence.

Automated summary

The study combined BICEP/Keck 2018 and Planck PR4 data to constrain the tensor-to-scalar ratio r consistently with the six parameters of the ΛCDM model, resulting in r < 0.032 at 95% confidence.