What does this research mean for the field?

The improved absolute polarization calibration method enhances the accuracy of measurements from the BICEP3 telescope, allowing for better detection of cosmic birefringence in the Cosmic Microwave Background. Novelty: ClaimNovelty.METHODOLOGICAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

What question did this study set out to answer?

This research aims to improve absolute polarization calibration methods for CMB polarimeters to address cosmic birefringence effects.

February 24, 2026

Improved Absolute Polarization Calibrator for BICEP CMB Polarimeters

Key Points

This research aims to improve absolute polarization calibration methods for CMB polarimeters to address cosmic birefringence effects.
Calibrated the BICEP3 telescope using a rotating polarized source.
Used the In-Situ Absolute Angle Calibrator (ISAAC) alongside the telescope for accurate measurements.
Analyzed the resulting data to break the degeneracy between birefringence and instrument polarization angles.
Achieved clearer and more accurate measurements of polarization from the Cosmic Microwave Background.
Successfully mitigated effects of cosmic birefringence on polarization readings.
Demonstrated improved correlation between instrument data and theoretical predictions.

Abstract

Cosmic birefringence is a hypothesized parity violation in electromagnetism that predicts a frequency-independent polarization rotation as light propagates. This would rotate the light from the Cosmic Microwave Background, producing an unexpected EB correlation. However, cosmic birefringence angle is degenerate with instrument polarization angle, and breaking this degeneracy requires an absolute polarization calibration. We calibrate the BICEP3 telescope (a 95GHz CMB polarimeter) by observing a rotating polarized source (RPS) with both the telescope and a small test receiver called the In-Situ Absolute Angle Calibrator (ISAAC).

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