# Negative- and positive-phase-velocity propagation in an isotropic chiral medium moving at constant velocity

## TL;DR

This paper investigates how electromagnetic plane waves behave in a moving isotropic chiral medium, revealing that phase velocity can appear positive or negative depending on the observer's frame of reference due to relativistic effects.

## Contribution

It demonstrates that phase velocity signs are frame-dependent in a moving chiral medium, using Lorentz transformations to analyze electromagnetic wave propagation.

## Key findings

- Positive phase velocity in co-moving frame can appear negative in non-co-moving frames.
- Negative phase velocity in co-moving frame can appear positive in non-co-moving frames.
- Electromagnetic wave behavior is affected by relativistic motion of the medium.

## Abstract

Analysis of electromagnetic planewave propagation in a medium which is a spatiotemporally homogeneous, temporally nonlocal, isotropic, chiral medium in a co-moving frame of reference shows that the medium is both spatially and temporally nonlocal with respect to all non-co-moving inertial frames of reference. Using the Lorentz transformations of electric and magnetic fields, we show that plane waves which have positive phase velocity in the co-moving frame of reference can have negative phase velocity in certain non-co-moving frames of reference. Similarly, plane waves which have negative phase velocity in the co-moving frame can have positive phase velocity in certain non-co-moving frames.