BICEP2 / Keck Array VI: Improved Constraints On Cosmology and
  Foregrounds When Adding 95 GHz Data From Keck Array
  We present results from an analysis of all data taken by the BICEP2 & Keck
Array CMB polarization experiments up to and including the 2014 observing
season. This includes the first Keck Array observations at 95 GHz. The maps
reach a depth of 50 nK deg in Stokes $Q$ and $U$ in the 150 GHz band and 127 nK
deg in the 95 GHz band. We take auto- and cross-spectra between these maps and
publicly available maps from WMAP and Planck at frequencies from 23 GHz to 353
GHz. An excess over lensed-LCDM is detected at modest significance in the
95x150 $BB$ spectrum, and is consistent with the dust contribution expected
from our previous work. No significant evidence for synchrotron emission is
found in spectra such as 23x95, or for correlation between the dust and
synchrotron sky patterns in spectra such as 23x353. We take the likelihood of
all the spectra for a multi-component model including lensed-LCDM, dust,
synchrotron and a possible contribution from inflationary gravitational waves
(as parametrized by the tensor-to-scalar ratio $r$), using priors on the
frequency spectral behaviors of dust and synchrotron emission from previous
analyses of WMAP and Planck data in other regions of the sky. This analysis
yields an upper limit $r_{0.05}<0.09$ at 95% confidence, which is robust to
variations explored in analysis and priors. Combining these $B$-mode results
with the (more model-dependent) constraints from Planck analysis of CMB
temperature plus BAO and other data, yields a combined limit $r_{0.05}<0.07$ at
95% confidence. These are the strongest constraints to date on inflationary
gravitational waves.
