Testing CPT Symmetry with Current and Future CMB Measurements

TL;DR

This paper uses current and future CMB data to test CPT symmetry by constraining polarization rotation effects, finding tentative evidence of CPT violation and exploring how future measurements can improve these constraints.

Contribution

It provides the first combined analysis of current CMB data for CPT violation and forecasts the improved constraints achievable with future Planck measurements.

Findings

Current data suggest a 2σ indication of CPT violation.

Upper limit on anisotropic rotation angle variance is 0.035 at 95% confidence.

Future Planck data can significantly tighten CPT violation constraints.

Abstract

In this paper we use the current and future cosmic microwave background (CMB) experiments to test the Charge-Parity-Time Reversal (CPT) symmetry. We consider a CPT-violating interaction in the photon sector $\mathcal{L}_{\rm cs}\sim p_\mu A_\nu \tilde{F}^{\mu\nu}$ which gives rise to a rotation of the polarization vectors of the propagating CMB photons. By combining the nine-year WMAP, BOOMERanG 2003 and BICEP1 observations, we obtain the current constraint on the isotropic rotation angle $\bar{\alpha} = -2.12 \pm 1.14$ ($1\sigma$), indicating an about $2\sigma$ significance of the CPT violation. Here, we particularly take the systematic errors of CMB measurements into account. Then, we study the effects of the anisotropies of the rotation angle [$\Delta{\alpha}({\bf \hat{n}})$] on the CMB polarization power spectra in detail. Due to the small effects, the current CMB polarization data can not constrain the related parameters very well. We obtain the 95\% C.L. upper limit of the variance of the anisotropies of the rotation angle $C^\alpha(0) < 0.035$ from all the CMB datasets. More interestingly, including the anisotropies of rotation angle could lower the best fit value of $r$ and relax the tension on the constraints of $r$ between BICEP2 and Planck. Finally, we investigate the capabilities of future Planck polarization measurements on $\bar{\alpha}$ and $\Delta{\alpha}({\bf \hat{n}})$. Benefited from the high precision of Planck data, the constraints of the rotation angle can be significantly improved.