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

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 gives rise to new collective electromagnetic modes characterized by distinct pairs of refractive indices associated with right- and left-handed circularly polarized waves. We analyze the optical behavior through the rotatory power (RP) and the 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 from radio pulsars to establish 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 ${10}^{\ensuremath{-}16}$ and ${10}^{\ensuremath{-}22}$, respectively.