  We consider the phenomenon of natural optical activity, and related chiral
magnetic effect in metals with low carrier concentration. To reveal the
correspondence between the two phenomena, we compute the optical conductivity
of a noncentrosymmetric metal to linear order in the wave vector of the light
wave, specializing to the low-frequency regime. We show that it is the orbital
magnetic moment of quasiparticles that is responsible for the natural optical
activity, and thus the chiral magnetic effect. While for purely static magnetic
fields the chiral magnetic effect is known to have a topological origin and to
be related to the presence of Berry curvature monopoles (Weyl points) in the
band structure, we show that the existence of Berry monopoles is not required
for the dynamic chiral magnetic effect to appear; the latter is thus not unique
to Weyl metals. The magnitude of the dynamic chiral magnetic effect in a
material is related to the trace of its gyrotropic tensor. We discuss the
conditions under which this trace is non-zero; in noncentrosymmetric Weyl
metals it is found to be proportional to the energy-space dipole moment of
Berry curvature monopoles. The calculations are done within both the
semiclassical kinetic equation, and Kubo linear response formalisms, with
coincident results.
