First CMB Constraints on Direction-Dependent Cosmological Birefringence from WMAP-7

TL;DR

This paper presents the first constraints on direction-dependent cosmological birefringence using WMAP-7 data, focusing on the rotation-angle power spectrum and its spatial fluctuations across the sky.

Contribution

It introduces a novel analysis of the rotation-angle power spectrum for multipoles up to 512, accounting for spatial variations in birefringence.

Findings

First CMB constraint on rotation-angle power spectrum for L=0 to 512

68% confidence upper limit of 1 degree on quadrupole of scale-invariant spectrum

Detection of no significant direction-dependent birefringence

Abstract

A Chern-Simons coupling of a new scalar field to electromagnetism may give rise to cosmological birefringence, a rotation of the linear polarization of electromagnetic waves as they propagate over cosmological distances. Prior work has sought this rotation, assuming the rotation angle to be uniform across the sky, by looking for the parity-violating TB and EB correlations a uniform rotation produces in the CMB temperature/polarization. However, if the scalar field that gives rise to cosmological birefringence has spatial fluctuations, then the rotation angle may vary across the sky. Here we search for direction-dependent cosmological birefringence in the WMAP-7 data. We report the first CMB constraint on the rotation-angle power spectrum for multipoles between L = 0 and L = 512. We also obtain a 68% confidence-level upper limit of 1 degree on the square root of the quadrupole of a scale-invariant rotation-angle power spectrum.