Photon-neutrino scattering and the B-mode spectrum of CMB photons

TL;DR

This paper calculates the contribution of photon-neutrino scattering to the B-mode polarization spectrum of the CMB, finding it negligible at low multipoles but significant at intermediate scales, impacting interpretations of primordial gravitational waves.

Contribution

It introduces a detailed calculation of photon-neutrino scattering effects on CMB B-mode polarization using the quantum Boltzmann equation, highlighting its importance at certain scales.

Findings

Photon-neutrino scattering contribution is negligible for small 

Significant at multipoles 50 to 200, affecting BICEP2 data interpretation

Implication for understanding the origin of observed B-mode spectrum

Abstract

On the basis of the quantum Boltzmann equation governing the time-evolution of the density matrix of polarized CMB photons in the primordial scalar perturbations of metric, we calculate the B-mode spectrum of polarized CMB photons contributed from the scattering of CMB photons and CNB neutrinos (Cosmic Neutrino Background). We show that such contribution to the B-mode spectrum is negligible for small $\ell$, however is significantly large for $50 < \ell< 200$ by plotting our results together with the BICEP2 data. Our study and results imply that in order to theoretically better understand the origin of the observed B-mode spectrum of polarized CMB photons ($r$-parameter), it should be necessary to study the relevant and dominate processes in both tensor and scalar perturbations.