Neutrino-Induced Polarization Rotation in Active Galactic Nuclei Plasmas

TL;DR

This paper investigates how an asymmetric neutrino background can cause parity-violating birefringence in AGN plasmas, leading to unique polarization rotation signatures that could help probe neutrino asymmetries.

Contribution

It introduces a new theoretical framework for detecting neutrino asymmetries through polarization rotation in AGN plasmas, distinct from magnetic field effects.

Findings

Anomalous frequency dependence of polarization rotation angle identified.

Largest predicted rotation angle is approximately 10^{-35} radians at X-ray frequencies.

Spectral signatures can potentially probe neutrino asymmetries independently of magnetic fields.

Abstract

We study parity-violating birefringence induced by an asymmetric neutrino background in plasmas associated with active galactic nuclei (AGN). We derive a directionality factor arising from the relative bulk motion between the neutrino medium and plasma, and show that it can produce an anomalous frequency dependence of the polarization-rotation angle, distinct from the $\omega^{-2}$ scaling of Faraday rotation. This anomalous scaling can occur either at the resonance plasma frequency condition $\omega \simeq \omega_p$, or when $E_\nu^{0}\simeq m_\nu \omega/\omega_p$ lies within the range of the neutrino energy spectrum. We estimate the effect for three scenarios: jets propagating through the cosmic neutrino background (C$\nu$B), jets with an internal flux of high-energy neutrinos, and accretion-disk plasma permeated by the C$\nu$B. Of the three scenarios, the latter gives the largest rotation angle $\phi_{\rm d} \sim 10^{-35}\,\mathrm{rad}$, at X-ray frequencies. Although the predicted rotation angles are below current polarimetric sensitivity, the identified spectral signatures provide a theoretical framework for probing neutrino asymmetries and AGN plasma properties independent of magnetic field models.