Cosmological CPT violation and CMB polarization measurements

Abstract

In this paper we study the possibility of testing Charge-Parity-TimeReversal (CPT) symmetry with cosmic microwave background (CMB)experiments. We consider two kinds of Chern-Simons (CS) term,electromagnetic CS term and gravitational CS term, and study theireffects on the CMB polarization power spectra in detail. Bycombining current CMB polarization measurements, the seven-yearWMAP, BOOMERanG 2003 and BICEP observations, we obtain a tightconstraint on the rotation angle Δα = −2.28±1.02 deg(1 σ), indicating a 2.2 σ detection of the CPTviolation. Here, we particularly take the systematic errors of CMBmeasurements into account. After adding the QUaD polarization data,the constraint becomes −1.34 < Δα < 0.82 deg at 95%confidence level. When comparing with the effect of electromagneticCS term, the gravitational CS term could only generate TB and EBpower spectra with much smaller amplitude. Therefore, the inducedparameter ϵ can not be constrained from the currentpolarization data. Furthermore, we study the capabilities of futureCMB measurements, Planck and CMBPol, on the constraints ofΔα and ϵ. We find that the constraint ofΔα can be significantly improved by a factor of 15.Therefore, if this rotation angle effect can not be taken intoaccount properly, the constraints of cosmological parameters will bebiased obviously. For the gravitational CS term, the future Planckdata still can not constrain ϵ very well, if the primordialtensor perturbations are small, r < 0.1. We need the more accurateCMBPol experiment to give better constraint on ϵ.