CMB Polarization by the Asymmetric Template of Scalar Perturbations

TL;DR

This paper investigates how a dipole asymmetric template in scalar perturbations affects CMB polarization, leading to modifications in electric and magnetic modes, with potential implications for detecting tensor perturbations.

Contribution

It introduces a novel approach to modeling CMB polarization by incorporating a dipole asymmetric scalar perturbation template, deriving explicit angular power spectra expressions.

Findings

Electric polarization is modified by the asymmetry.

Magnetic polarization is generated due to the asymmetry.

Large-scale B-mode spectrum resembles that from tensor perturbations with r≈0.005.

Abstract

Inspired by a dipole asymmetric template for the CMB temperature map in the primordial scalar fluctuations observed by Planck at a large scale, we examine the contribution of a similar template for power asymmetry in modifying the linear polarization pattern of CMB. Replacing un-modulated temperature fluctuation with dipolar modulated one in time evolution equations somehow breaks linear perturbation in the various components of the CMB map. This non-linearity allows deflecting CMB polarization in patterns that contain divergence-free components. The explicit expressions for the angular power spectra of the electric and magnetic-type parities of linear polarization are derived in the form of the line of sight integral solutions. Our results demonstrate that the electric-type polarization is modified and the magnetic-type polarization would be produced. Such imprints depend on the linear and square of the asymmetric amplitude for $E$- and $B$-modes power spectra, respectively. For the observed dipole template, the value of $B$ polarization spectrum at the large scale ($\ell\lesssim 10$) is almost equivalent to the power spectrum obtained from Compton scattering in the presence of tensor perturbation with tensor to scalar ratio about $r\simeq0.005$.