NP Stokes fields for radio astronomy

TL;DR

This paper introduces NP Stokes fields within the Newman-Penrose formalism, providing a rigorous foundation for analyzing electromagnetic polarization, especially relevant to cosmic microwave background studies and Lorentz transformations.

Contribution

It establishes NP Stokes fields as the NP formalism equivalent of Stokes parameters, enhancing the theoretical framework for polarization analysis in cosmology.

Findings

Defines NP Stokes fields as NP formalism counterparts to Stokes parameters

Relates SWSH applications in cosmology to NP formalism

Facilitates computation of Lorentz transformation properties of polarization

Abstract

The spin weighted spherical harmonic (SWSH) description of angular functions typically is associated with the Newman-Penrose (NP) null tetrad formalism. Recently the SWSH description, but not the NP formalism, has been used in the study of the polarization anisotropy of the cosmic microwave background. Here we relate this application of SWSHs to a description of electromagnetic radiation and polarization in the NP formalism. In particular we introduce NP Stokes fields that are the NP equivalent of the Stokes parameters. In addition to giving a more coherent foundation for the recent cosmological SWSH application, the NP formalism aids in the computation of the Lorentz transformation properties of polarization.