SPIDER: Looking for CMB B-mode Polarization Behind the Galactic Screen

Aurelien Fraisse (Princeton U.)

Current cosmological data strongly favor a simple flat power-law LCDM model of the Universe. However, there is no *direct* evidence to date for the cornerstone of this model: inflation. Although the inflationary paradigm explains a wide range of physical observations, alternatives, such as the ekpyrotic scenario, can do as much while avoiding some of the difficulties associated with building "natural" models of inflation. A unique prediction of inflation is the presence of a primordial divergence-free polarization pattern ("B-modes") in the Cosmic Microwave Background (CMB). SPIDER is a balloon-borne CMB polarization experiment designed to look for this signal and to either detect it or set stringent constraints on the tensor-to-scalar ratio r which determines its amplitude. I will present a status report on the SPIDER mission, whose first flight is scheduled to take off from McMurdo, Antarctica in December 2012, with a heavy focus on the issue of polarized Galactic foregrounds. In the SPIDER field, and more generally over the entire sky accessible from a McMurdo long-duration balloon flight, the polarized emission from interstellar dust is expected to be as bright or brighter than a r=0.03 B-mode signal at all frequencies and angular scales of interest. I will present a publicly available set of templates for this emission, and confront it to our theoretical and observational understanding of interstellar dust, which constrains both its polarization amplitude and direction.