New tests of parity violation in the early universe

by Dr Claire Rigouzzo (KCL)

Monday Feb 23, 2026, 3:00 PM → 4:00 PM Europe/Madrid

C7b/058 - Seminar (IFAE Main Building C7b)

Precise polarization measurements of the Cosmic Microwave Background (CMB) provide an opportunity to rigorously test the standard cosmological model. The correlation between $E$ and $B$ modes is expected to arise from parity-violating physics in the Universe. However, detecting these $EB$ correlations remains extremely challenging as it demands exceptionally precise polarization calibration of observational instruments. In this work, we present a novel calibration method for CMB polarimeters that circumvents the need for external polarized sources or self-calibration techniques. By cross-correlating data from two instruments observing the same region of the sky, we demonstrate that the difference between their misalignment angles can be resolved with data only, providing an assumption free calibration technique. Leveraging the high-precision polarization calibration expected for the Simons Observatory Small Aperture Telescopes, we show that can calibrate other instruments observing overlapping sky regions. As a proof of concept, we demonstrate that this approach yields a polarization angle calibration of $0.15^\circ$ for the Simons Observatory Large Aperture Telescope and $0.31^\circ$ for Planck at 143 GHz, without requiring assumptions about cosmic birefringence or the primordial EB spectrum. In comparison, other assumption-free method like using astrophysical polarised sources reach a precision of the order of $0.5^\circ$. This improved calibration can be directly applied to searches for parity-violating signals such as isotropic cosmic birefringence or a chiral primordial tensor component.