Improved limits on the tensor-to-scalar ratio using BICEP and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>P</mml:mi><mml:mi>l</mml:mi><mml:mi>a</mml:mi><mml:mi>n</mml:mi><mml:mi>c</mml:mi><mml:mi>k</mml:mi></mml:math> data
M. Tristram, A. J. Banday, K. M. Górski, Reijo Keskitalo, C. R. Lawrence, K. J. Andersen, R. B. Barreiro, J. Borrill, L. P. L. Colombo, H. K. Eriksen, R. Fernández-Cobos, Theodore Kisner, E. Martínez-González, B. Partridge, D. Scott, T. L. Svalheim, I. K. Wehus
Abstract
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 $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. We discuss the sensitivity of constraints on $r$ to uncertainties in the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ parameters as defined by the Planck data. In particular, we are able to derive a constraint on the reionization optical depth $\ensuremath{\tau}$ 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.