Probing CPT Violation with CMB Polarization Measurements

TL;DR

This paper measures the polarization rotation of CMB photons to test CPT symmetry, finding a potential violation at 3 sigma significance with current data, and providing improved constraints on CPT violation.

Contribution

The study provides the first combined analysis of multiple CMB datasets to constrain CPT violation via polarization rotation, achieving the most stringent limits to date.

Findings

Combined data suggests a 3 sigma indication of CPT violation.

Individual datasets show varying signs and uncertainties in polarization rotation.

New constraints significantly tighten previous limits on CPT violation.

Abstract

The electrodynamics modified by the Chern-Simons term $\mathcal{L}_{cs}\sim p_{\mu}A_{\nu}\tilde F^{\mu\nu}$ with a non-vanishing $p_{\mu}$ violates the {\it Charge-Parity-Time Reversal} symmetry (CPT) and rotates the linear polarizations of the propagating {\it Cosmic Microwave Background} (CMB) photons. In this paper we measure the rotation angle $\Delta\alpha$ by performing a global analysis on the current CMB polarization measurements from the {\it seven-year Wilkinson Microwave Anisotropy Probe} (WMAP7), {\it BOOMERanG 2003} (B03), BICEP and QUaD using a Markov Chain Monte Carlo method. Neglecting the systematic errors of these experiments, we find that the results from WMAP7, B03 and BICEP all are consistent and their combination gives $\Delta\alpha=-2.33\pm0.72~{\rm deg}~(68\%~C.L.)$, indicating a $3\,\sigma$ detection of the CPT violation. The QUaD data alone gives $\Delta\alpha=0.59\pm0.42~{\rm deg}~(68\%~C.L.)$ which has an opposite sign for the central value and smaller error bar compared to that obtained from WMAP7, B03 and BICEP. When combining all the polarization data together, we find $\Delta\alpha=-0.04\pm0.35~{\rm deg}~(68\%~C.L.)$ which significantly improves the previous constraint on $\Delta\alpha$ and test the validity of the fundamental CPT symmetry at a higher level.