Illustration of evolution of the universe from the Big Bang (left). In this diagram the universe is represented in two dimensions and the third (horizontal) dimension is time, increasing to the right.
B-mode polarization of the Cosmic Microwave Background (CMB) is an inescapable consequence of the current cosmological paradigm. In addition to generating the initial density perturbation spectrum, an inflationary epoch will create gravitational waves that should leave a unique and potentially detectable signature of B-mode polarization in the CMB. In turn, detection of these modes would provide important information about the scale and shape of the inflationary potential. Numerous experiments, including the KICP’s SPT and BICEP/Keck Array efforts, are targeting this polarization signature. The goal of the CMB Polarization Hub is to coordinate and synthesize results from a number of experiments searching for B-mode polarization in order to minimize systematic errors due to backgrounds and maximize signal. With these combined results in hand, the probability of detection is maximized or the very strongest possible limits on inflationary gravitational waves will be established.

BICEP2 and The Keck Array at the South Pole.
Four CMB experiments located in the Atacama desert in Chile (QUIET, Polarbear, ABS, and ACT) and two at the South Pole (SPT and BICEP/Keck) are participating in the Hub. The QUIET collaboration has already performed observations in four different fields in the sky. The remaining three Atacama experiments have agreed to target these same four fields so that the data can be compared and combined in the joint analysis. Between the four experiments, five different wavelength bands will be studied, with each of the experiments tackling the observations in a different manner. Using these deep, multiple frequency observations is essential in order to understand and eliminate galactic foreground contamination and other systematic errors. In addition to the four fields specific to the Atacama experiments, the SPT has identified a particularly clean field for those experiments and the two at the South Pole to target. A joint analysis including data from all six experiments can then be carried out further constraining backgrounds and systematic errors.

South Pole Telescope (SPT).
The goal of the CMB Polarization Hub at the KICP is to provide unprecedented accuracy in the measurement of a number of important cosmological parameters. For example, the ratio of Scalar-to-Tensor perturbations, r, should be determined if it is greater than about 0.01. To accomplish this goal, the hub will bring together experimentalists, and the data from their experiments, for a joint analysis. Members of the various experimental teams will visit the KICP to accomplish this program. Each experiment will publish their own results and data but will also provide their resulting maps, and simulated maps convolved with their experiment’s unique profile, to the hub. These maps will be combined and then used to eliminate galactic foregrounds and constrain systematic errors. The final deliverable of the hub will be the combined power spectra and associated cosmological parameters, presented in a form that is useful for the cosmology community.