CMB Polarization Systematics Due to Beam Asymmetry: Impact on Cosmological Birefringence

TL;DR

This paper investigates how beam asymmetry systematics in CMB polarization measurements can mimic signals of cosmological birefringence, affecting the interpretation of parity violation and polarization rotation in upcoming experiments.

Contribution

It analyzes the impact of beam systematics on polarization rotation measurements, highlighting potential contamination in detecting fundamental physics signals.

Findings

Beam asymmetries can induce false TB and EB correlations.

Optimized experiment design reduces systematic contamination.

Implications for future constraints on parity-violating physics.

Abstract

The standard cosmological model is assumed to respect parity symmetry. Under this assumption the cross-correlations of the CMB'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 CMB 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.