UC San Diego researchers developed a calibration method to test whether a suspected twist in the cosmic microwave background is real or caused by detector-orientation errors. It compares maps from different detector groups, but cannot determine the absolute rotation on its own.
Tested on eight polarization maps from the European Space Agency’s Planck satellite, the method closely agreed with the Minami-Komatsu analysis, despite relying on different assumptions. Because it cannot measure a rotation shared by all maps, the team anchored its results to that analysis’s calibration and reproduced a cosmic-birefringence angle of 0.37 degrees, plus or minus 0.12 degrees, matching prior findings.
Calibration errors can also mimic primordial B-mode polarization, a curl-like pattern in the cosmic microwave background that would provide strong evidence for gravitational waves from cosmic inflation. The researchers said future B-mode detections would need to withstand this kind of scrutiny as instruments become more sensitive.
