Positive-, negative-, and orthogonal-phase-velocity propagation of electromagnetic plane waves in a simply moving medium: Reformulation and reappraisal

Reformulating the issue of planewave propagation in a simply moving, dielectric-magnetic medium that is isotropic in the co-moving reference frame, using the Lorentz transformations of electric and magnetic fields and not the Minkowski constitutive relations–we reaffirm 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. Furthermore, this phenomenon occurs whether the medium is dissipative or not. For a fixed propagation direction, orthogonal phase velocity arises only at a unique velocity of the non-co-moving frame.