B-mode CMB Polarization from Patchy Screening during Reionization

TL;DR

This paper investigates the B-mode polarization of the CMB caused by patchy reionization, revealing that screening effects dominate at small scales while scattering effects are more significant at larger scales.

Contribution

It introduces the first calculation of the screening contribution to B-mode polarization from patchy reionization, highlighting its importance at small scales.

Findings

Screening B-modes surpass scattering B-modes at scales larger than the acoustic scale.

The ratio of screening to scattering B-modes approaches 2.5 below the damping scale.

Screening B-modes are subdominant at degree scales relevant for gravitational wave detection.

Abstract

B-modes in CMB polarization from patchy reionization arise from two effects: generation of polarization from scattering of quadrupole moments by reionization bubbles, and fluctuations in the screening of E-modes from recombination. The scattering contribution has been studied previously, but the screening contribution has not yet been calculated. We show that on scales smaller than the acoustic scale (l>300), the B-mode power from screening is larger than the B-mode power from scattering. The ratio approaches a constant ~2.5 below the damping scale (l>2000). On degree scales relevant for gravitational waves (l<100), screening B-modes have a white noise tail and are subdominant to the scattering effect. These results are robust to uncertainties in the modeling of patchy reionization.