Rotation of the polarization vector from distant radio galaxies in the perturbed FRW metric

TL;DR

This paper investigates how large-scale scalar perturbations in the universe's metric can cause a dipolar anisotropy in the polarization vectors of distant radio galaxies, potentially explaining observed correlations.

Contribution

It introduces a formalism to calculate polarization rotation due to scalar perturbations in the FRW metric, linking theoretical predictions to observed anisotropies.

Findings

Rotation depends on the galaxy's angular position, matching observed dipole patterns.

Scalar perturbations can produce polarization alignments over large scales.

The model qualitatively reproduces the observed anisotropic correlations.

Abstract

Analysis of the correlation between the angular positions of distant radio galaxies on the sky and the orientations of their polarization vectors with respect to their major axes, indicates a dipolar anisotropy in the large scale. We consider a single mode of large-scale scalar perturbation to the FRW metric. Using Newman-Penrose formalism, we calculate the rotation of the galaxy major axis with respect to the polarization vector as the elliptic image and the polarization vector are carried through the perturbed space-time. The dependence of the rotation on the polar angular coordinate of the galaxy, is qualitatively similar to the claimed dipole pattern.