Analysis Challenges in Scanning CMB Missions: Beam Asymmetry

Precise measurement of angular power spectrum of the Cosmic Microwave Background (CMB) can accurately constrain many cosmological models and parameters. Over the last decade, measurements of CMB anisotropy has spearheaded the remarkable transition of cosmology into a precision science. However, increasingly sensitive, high resolution, `full' sky measurements from different CMB experiments also pose a stiff  challenge to current analysis techniques. The analysis techniques must not only be computationally fast to contend with the huge size of the data, but, the higher sensitivity also limits the simplifying assumptions which  could then be invoked to achieve the desired speed without compromising  the final precision goals. The effect of asymmetric beams is perhaps the  most important systematic effect in the current and future CMB missions, like Planck, which involve a significant effort on polarization measurement. Accounting for this systematic effect is a major challenge in CMB analysis. We have developed and implemented a very fast pixel based convolution method, that includes real instrumental beams and scan  strategy, by pre-computing the (varying) shape of the `effective' beams across the sky. Which, in turn, leads to fast Monte Carlo simulations and realistic semi-analytic approaches to account for the systematic effect.  This presentation will be centered on the current Planck mission and its analysis challenges, with special emphasis on the systematic effect of  beams.