Asymmetric beams in cosmic microwave background anisotropy experiments

We propose a new formalism to handle asymmetric beams in the data analysis of cosmic microwave background anisotropy experiments. For any beam shape, the formalism finds the optimal circularly symmetric equivalent and is thus easily adaptable to existing data analysis methods. We demonstrate certain key points by using a simulated highly elliptic beam and the beams and dat a of the MAXIMA-1 experiment, where the asymmetry is mild. We show that in both cases the formalism does not bias the angular power spectrum estimates . We analyze the limitations of the formalism and find that it is well suit ed for most practical situations.