Chiral Maxwell waves in continuous media from Berry monopoles

We propose a method to predict the existence of topologically protected electromagnetic chiral modes between continuous media described by Maxwell's equations. The number and character of these modes is related to topological charges (Berry monopoles) in parameter space. Unlike the approaches proposed so far, our description does not require a regularization parameter at large $\mathbf{k}$ nor the materials to be topological on their own. The predictions of the theory are confirmed by additional numerical simulations of interfaces of gyrotropic media.