Precision Tests of Parity Violation Over Cosmological Distances

TL;DR

This paper discusses how improved calibration of CMB polarization measurements can enable the detection of parity-violating physics, such as cosmic polarization rotation, using current and future experiments.

Contribution

It introduces the CalSat space-based calibrator to significantly enhance polarization angle calibration accuracy for CMB experiments, facilitating tests of fundamental physics.

Findings

CalSat can achieve 0.05° calibration accuracy.

Current CMB polarimeters can be repurposed to detect parity violation.

Enhanced calibration improves sensitivity to cosmic polarization rotation.

Abstract

Recent measurements of the Cosmic Microwave Background $B$-mode polarization power spectrum by the BICEP2 and POLARBEAR experiments have demonstrated new precision tools for probing fundamental physics. Regardless of origin, the fact that we can detect sub-$\mu$K CMB polarization represents a tremendous technological breakthrough. Yet more information may be latent in the CMB's polarization pattern. Because of its tensorial nature, CMB polarization may also reveal parity-violating physics via a detection of cosmic polarization rotation. Although current CMB polarimeters are sensitive enough to measure one degree-level polarization rotation with $>5\sigma$ statistical significance, they lack the ability to differentiate this effect from a systematic instrumental polarization rotation. Here, we motivate the search for cosmic polarization rotation from current CMB data as well as independent radio galaxy and quasar polarization measurements. We argue that an improvement in calibration accuracy would allow the precise measurement of parity- and Lorentz-violating effects. We describe the CalSat space-based polarization calibrator that will provide stringent control of systematic polarization angle calibration uncertainties to $0.05^\circ$ -- an order of magnitude improvement over current CMB polarization calibrators. CalSat-based calibration could be used with current CMB polarimeters searching for $B$-mode polarization, effectively turning them into probes of cosmic parity violation, i.e. without the need to build dedicated instruments.