New Extraction of the Cosmic Birefringence from the Planck 2018 Polarization Data (2011.11254v1)

Abstract: We search for evidence of parity-violating physics in the Planck 2018 polarization data, and report on a new measurement of the cosmic birefringence angle, $\beta$. The previous measurements are limited by the systematic uncertainty in the absolute polarization angles of the Planck detectors. We mitigate this systematic uncertainty completely by simultaneously determining $\beta$ and the angle miscalibration using the observed cross-correlation of the $E$- and $B$-mode polarization of the cosmic microwave background and the Galactic foreground emission. We show that the systematic errors are effectively mitigated and achieve a factor-of-$2$ smaller uncertainty than the previous measurement, finding $\beta=0.35 \pm 0.14\,\deg$ (68% C.L.), which excludes $\beta = 0$ at $99.2$% C.L. This corresponds to the statistical significance of $2.4\sigma$.

• The paper achieves a factor-of-two uncertainty reduction by simultaneously extracting the cosmic birefringence angle and correcting detector miscalibration.
• It reports a 0.35° birefringence angle at 68% confidence, excluding the null hypothesis with a 99.2% confidence level.
• Robust validation with end-to-end simulations supports its implications for new parity-violating physics beyond the standard model.

Overview of "New Extraction of the Cosmic Birefringence from the Planck 2018 Polarization Data"

This paper presents an updated analysis of cosmic birefringence based on the polarization data acquired by the Planck satellite in 2018. The authors, Minami and Komatsu, focus on refining the measurement of the cosmic birefringence angle, denoted as $\beta$, which is pertinent in investigating parity-violating physics beyond the standard model (SM) of particle physics. Their approach effectively mitigates the systematic uncertainty associated with the absolute polarization angles of the Planck detectors by implementing a simultaneous determination of the cosmic birefringence angle and the angle miscalibration using the observed cross-correlation of the $E$- and $B$-mode polarization from the Cosmic Microwave Background (CMB) and the Galactic foreground emissions.

The methodology employed achieves a factor-of-two reduction in uncertainty, yielding $\beta=0.35 \pm 0.14^\circ$ at a 68% confidence level, which notably excludes the null hypothesis, $\beta=0$, with a high confidence level of 99.2%. This $2.4\sigma$ deviation from zero may suggest the presence of new physics, potentially linked to axionlike particles affecting the cosmic polarization through a Chern-Simons coupling in the Lagrangian density, resulting in a non-zero $EB$ correlation that violates parity.

Methodological Advancements

The advancement introduced in this work primarily relies on differentiating the polarization rotation effects caused by cosmic birefringence from those arising due to detector miscalibration. The paper elucidates how simultaneous measurements of $\beta$ and $\alpha_\nu$ (miscalibration angles for different frequencies) can be accomplished by leveraging the different frequency and multipole dependencies of the intrinsic CMB and foreground polarization power spectra. By adopting power spectra from cross-frequency maps across Planck's High Frequency Instrument (HFI) channels, the paper leverages the Planck 2018 data with a precision-focused approach that reduces collateral uncertainties.

Results and Potential Bias Mitigation

The paper's robustness is validated against the Planck end-to-end simulations, ensuring minimal instrument-induced biases. The miscalibration angles $\alpha_\nu$ for different frequencies were verified to be consistent with zero, validating the calibration approach to within $1\sigma$, further confirming that the results of $\beta$ are not significantly skewed by instrumental errors. Moreover, tests excluding specific frequency channels (such as 100 GHz) demonstrated no significant change in the birefringence outcome, bolstering the assertion that observed effects are not artifacts of synchrotron $EB$ correlation at lower frequencies.

Implications and Future Directions

The determination of a non-zero cosmic birefringence angle holds substantial implications for theoretical physics, offering potential insights into parity violation phenomena and dark matter composition through axionlike fields. Further validation through independent observations and upcoming CMB polarization experiments could substantiate these findings and refine constraints on parity-violating models, potentially revealing new aspects of fundamental physics.

Moving forward, the focus would be on reducing systematic uncertainties inherent in current polarization measurements and exploring more sensitive CMB surveys to decisively confirm or refute the presence of cosmic birefringence, a stepping stone towards unveiling new physics beyond the standard cosmological model.