Hypothesis of a bi-isotropic-like plasma permeating the interstellar space

TL;DR

This paper explores electromagnetic wave propagation in a magnetized chiral plasma model of interstellar space, revealing exotic optical effects and constraining chiral parameters using pulsar data.

Contribution

It introduces a bi-isotropic-like plasma model for interstellar space and derives new electromagnetic modes and optical signatures, with astrophysical constraints on chiral parameters.

Findings

Finite chiral parameter causes double rotatory power sign reversal.

Modified helicon wave with right-handed polarization in low-frequency regime.

Upper limits on chiral parameter magnitude from pulsar data.

Abstract

In this work, we study the propagation of electromagnetic waves in a magnetized chiral plasma that pervades the interstellar space. The Maxwell equations, supplemented by bi-isotropic-like constitutive relations, are rewritten to describe a cold, uniform, and collisionless plasma model that yields new collective electromagnetic modes for distinct pairs of refractive indices associated with right- and left-handed circularly polarized waves. We have investigated the optical behavior through the rotatory power (RP) and dichroism coefficient, reporting that the finite chiral parameter induces double RP sign reversal, an exotic optical signature that takes place in chiral dielectrics and rotating plasmas. In the low-frequency regime, a modified propagating helicon with right-handed circular polarization is obtained. Next, supposing that the interstellar medium behaves as a chiral bi-isotropic-like cold plasma, we employ Astrophysical data of radio pulsars to achieve upper limits on the magnetoelectric parameters magnitude. In particular, by using dispersion measure and rotation measure data from five pulsars, we constrain the magnitude of the chiral parameter to the order of $10^{-16}$ and $10^{-22}$, respectively.