The B-mode polarization of CMB and Cosmic Neutrino Background

TL;DR

This paper investigates how the weak interaction between the Cosmic Neutrino Background and CMB contributes to B-mode polarization, offering a new method to probe the CNB through polarization measurements.

Contribution

It introduces the analysis of CNB's effect on B-mode polarization, expanding understanding beyond standard Compton scattering effects in scalar and tensor perturbations.

Findings

CNB contributes to B-mode polarization power spectrum

B-mode spectrum can serve as an indirect probe of CNB

Effects influence the tensor-to-scalar ratio estimation

Abstract

It is known that in contrast with the E-mode polarization, the B-mode polarization of the Cosmic Microwave Background cannot be generated by the Compton scattering in the case of scalar mode of metric perturbation. However it is possible to generate the B-mode by the Compton scattering in the case of tensor mode of metric perturbation. For this reason, the ratio of tensor to scalar modes of metric perturbation ($r\sim C_{Bl}/C_{El}$) is estimated by comparing the B-mode power spectrum with the E-mode at least for small $l$. We study the CMB polarization specially B-mode due to the weak interaction of Cosmic Neutrino Background (CNB) and CMB, in addition to the Compton scattering in both cases of scalar and tensor metric perturbations. It is shown that the power spectrum $C_{Bl}$ of the B-mode polarization receives some contributions from scalar and tensor modes, which have effects on the value of $r$-parameter. We also show that the B-mode polarization power spectrum can be used as an indirect probe into the CNB.