Measurements of B-mode Polarization at degree angular scales with the BICEP2, Keck, and Planck

The theory of cosmic inflation postulates that the initial conditions of our observable universe arose from quantum fluctuations during a very early burst of exponential expansion. The BICEP / Keck Array experiments are a series of cosmic microwave background (CMB) polarimeters specifically designed to search for gravitational waves predicted by inflation by looking for the faint B-mode patterns they would imprint on degree-scale CMB polarization. Observing from the South Pole between 2010 and 2012, the BICEP2 telescope made maps of unprecedented sensitivity at degree angular scales over 2\% of the sky, In March 2014 the BICEP2 team reported a high signal-to-noise detection of B-mode polarization at 150 GHz, at a level well above typical predictions of galactic foreground models for that region of sky, and consistent with a large contribution from inflationary gravitational waves. However, later last year high-frequency results reported by the Planck satellite indicated levels of polarized emission from galactic dust potentially high enough to account for the entire BICEP2 signal. In a recently published joint analysis that combines data from BICEP2, the Keck Array, and the Planck satellite, we find that there is not currently significant evidence for a gravitational wave signal, and we set the tightest constraints yet on its possible level. The outlook for continued progress using ultra-deep maps at multiple frequencies is strong. I will describe our current results and the continuing hunt for inflationary gravitational waves both with the BICEP / Keck Array experimental program and with future efforts.