Negative phase velocity in a uniformly moving, homogeneous, isotropic, dielectric-magnetic medium

Homogeneous, isotropic mediums characterized by relative permittivity scalars ∈ = ∈_R + i∈_I (∈R, ∈ _I ∈ R) and relative permeability scalars μ= μ_R + iμ_I (μ_R, μ_I μ_R μ_RR) are well known to support the propagation of plane waves with negative phase velocity (NPV), provided that both μ_R < 0 and μ_R < 0, We demonstrate that mediums which do not support NPV propagation when viewed at rest (e.g., mediums with μ_R > 0 and μ_R > 0), can support NPV propagation when they are viewed in a reference frame which is uniformly translated at a sufficiently high velocity. Representative numerical examples are used to explore the constitutive parameter regimes which support NPV propagation under the uniform-velocity condition.