Circular polarization of the cosmic microwave background induced by the optical Magnus effect on gravitational lensing

TL;DR

This paper proposes that the optical Magnus effect in gravitational lensing can induce circular polarization in the CMB, revealing a new fundamental mechanism for polarization generation.

Contribution

It introduces the optical Magnus effect as a novel mechanism for generating circular polarization in the CMB through gravitational lensing.

Findings

Circular polarization can be induced in the CMB by the optical Magnus effect.

The effect depends on the transverse shift of light trajectories based on helicity.

Current detection of this polarization is beyond reach.

Abstract

Polarization of the cosmic microwave background (CMB) brings out information not only on the early universe but also on the late-time large-scale structure via weak gravitational lensing. Here, we show that circular polarization is induced in principle from CMB temperature fluctuations when the optical Magnus effect is incorporated into gravitational lensing. This is a consequence of the transverse shift of a trajectory of light depending on its helicity that requires right-handed and left-handed components at the same observation point to be sourced from different points of the surface of last scattering. Whereas the resulting circular polarization is found far beyond the scope of current detection, our work establishes the optical Magnus effect on gravitational lensing as a new fundamental mechanism to produce circular polarization of CMB.