Elasticity theory for the CDW is considerably simplified by the strong anisotropy. In particular, since the electrons in the CDW are essentially confined on the chains, we need only keep track of displacements in the x-direction, i.e. along the most conducting axis. Because of this simplicity, we may define instead a single, dimensionless phase by , where is the displacement along the x direction. By a rescaling of axes, we may then write the elastic CDW Hamiltonian as
where K is the elastic stiffness.