Hydrodynamics of Cholesterics in an Extenal Magnetic Field

-Linearized hydrodynamical equations for a cholesteric liquid crystal with anisotropic magnetic permeability less than zero in an external magnetic field are derived. The mode structure in the absence of dissipation is determined. There is a transverse shear mode for directions of propagation perpendicular to the pitch axis with sound velocity where H is the external field, ρ the mass density, μa the magnitude of the anisotropic permeability, q0 2π over the pitch, and K1 and Ks are Frank elastic constants.