Beam mismatch effects in cosmic microwave background polarization measurements

¹ APC, Université Paris 7, CNRS/IN2P3, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France e-mail: [delabrouille;kaplan;ygh]@apc.univ-paris7.fr
² LAL, Université Paris-Sud 11, CNRS/IN2P3, BP 34, 91898 Orsay Cedex, France e-mail: rosset@lal.in2p3.fr
³ Experimental Physics Department, National University of Ireland, Maynooth, Co. Kildare, Ireland e-mail: [amurphy;v.yurchenko]@may.ie
⁴ LERMA, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France e-mail: jean-michel.lamarre@obspm.fr

Received: 22 October 2004
Accepted: 6 December 2006

Abstract

Measurement of cosmic microwave background polarization is today a major goal of observational cosmology. The level of the signal to measure, however, makes it very sensitive to various systematic effects. In the case of Planck, which measures polarization by combining data from various detectors, the beam asymmetry can induce a conversion of temperature signals to polarization signals or a polarization mode mixing. In this paper, we investigate this effect using realistic simulated beams and propose a first-order method to correct the polarization power spectra for the induced systematic effect.