Circular polarization of cosmic photons due to their interactions with Sterile neutrino dark matter

TL;DR

This study investigates how interactions between cosmic photons and sterile neutrino dark matter can induce circular polarization, providing potential observational signatures in gamma-ray bursts, galactic radio sources, and the CMB.

Contribution

It introduces a model for photon polarization conversion via sterile neutrino interactions and estimates the resulting Faraday conversion and CMB polarization signals across different astrophysical sources.

Findings

Faraday conversion angles are estimated to be between 10^{-3} and 10^{-18} radians for GRB photons.

Circular polarization power spectrum in the CMB can reach up to 0.01 Nano-Kelvin squared for certain mixing angles.

Interactions could produce observable circular polarization signatures in cosmic photon observations.

Abstract

In this paper, we explore the possibility of the polarization conversion of a wide energy range of cosmic photons to the circular polarization through their interactions with right handed Sterile neutrinos as a candidate for dark matter. By considering the Sterile neutrino in the seesaw mechanism framework and right-handed current model, we examine the Faraday conversion $\Delta \phi_\text{\tiny{FC}}$ of gamma ray burst (GRB) photons at both the prompt and afterglow emission levels as well as the radio photons emitted from our galaxy and extra-galactic sources interacting with the Sterile neutrinos. Consequently, for the Sterile neutrino with mixing angle $\theta^2\lesssim 10^{-2}$ motivated by models with a hidden sector coupled to the sterile neutrino, the Faraday conversion can be estimated as $\Delta \phi_\text{\tiny{FC}}\lesssim 10^{-3}-10^{-18}$ rad for GRB, $\Delta \phi_\text{\tiny{FC}}\lesssim 10^{-6}-10^{-11}$ rad for radio emission source from our galaxy and $\Delta \phi_\text{\tiny{FC}}\lesssim 10^{-6}-10^{-15}$ rad for extra-galactic sources. We also examine the V-mode power spectrum $C_{Vl}$ of the cosmic microwave background (CMB) at the last scattering surface. We show that the circular polarization power spectrum at the leading order is proportional to the linear polarization power spectrum $C_{pl}$ and the mixing angle where for $\theta^2\lesssim 10^{-2}$ leads to $C_{Vl}\lesssim 0.01$ Nano-Kelvin squared.