CMB polarization systematics due to beam asymmetry: Impact on cosmological birefringence

Abstract

The standard cosmological model is assumed to respect parity symmetry. Under this assumption the cross correlations of the cosmic microwave background's temperature anisotropy and ``gradient''-like polarization, with the ``curl''-like polarization, identically vanish over the full sky. However, extensions of the standard model which allow for light scalar field or axion coupling to the electromagnetic field, or coupling to the Riemann gravitational field strength, as well as other modifications of field theories, may induce a rotation of the cosmic microwave background polarization plane on cosmological scales and manifest itself as nonvanishing $TB$ and $EB$ cross correlations. Recently, the degree of parity violation (reflected in polarization rotation) was constrained using data from BOOMERANG, WMAP, and QUAD. Forecasts have been made for near-future experiments (e.g. PLANCK) to further constrain parity- and Lorentz-violating terms in the fundamental interactions of nature. Here we consider a real-world effect induced by a class of telescope beam systematics which can mimic the rotation of polarization plane or otherwise induce nonvanishing $TB$ and $EB$ correlations. In particular, adopting the viewpoint that the primary target of future experiments will be the inflationary $B$-mode signal, we assume the beam systematics of the upcoming PLANCK and POLARBEAR experiments are optimized towards this goal, and explore the implications of the allowed levels of beam systematics on the resulting precision of polarization-rotation measurements.