Eiichiro Komatsu and Yuto Minami talk about their recent work, first devising a way to extract a parity violating signature in the cosmic microwave background (i.e. birefringence) and then measuring it in Planck 2018 data.

They get a 2.4 sigma hint of a result, which is “important, if true”.

This signal is measured via correlation of E mode and B mode polarisation in the CMB. If the universe is birefringent then E mode polarisation would change into B mode and there would be a non-zero correlation between the two measured modes. Unfortunately, if the detector angle on the telescope wasn’t calibrated perfectly this would mimic the interesting signal. Yuto and Eiichiro’s new method is to measure this detector angle by looking at the E-B correlation in the foregrounds, where the light hasn’t travelled far enough to be affected by any potential birefringence in the universe.

This allows them to partially distinguish between the two types of measured E-B correlation. And with this method they get the hint of a signal for the new physics in the Planck 2018 data.

The method can be applied to the data from all other telescopes that have measured the polarisation of the microwave background and can therefore be confirmed, ruled out, or at least examined by SPT, ACT, Polarbear, etc.

Yuto and Eiichiro are also working with Planck to see if they can further rule out other systematics, e.g. an intrinsic E-B correlation in the foreground polarisation.

Yuto: https://orcid.org/0000-0003-2176-8089
Eiichiro: https://wwwmpa.mpa-garching.mpg.de/~komatsu/

Paper: https://arxiv.org/abs/2011.11254
Published on PRL: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.221301
The slides: https://wwwmpa.mpa-garching.mpg.de/~komatsu/presentation/cosmotalk_birefringence.pdf

Talk date: Nov. 23, 2020