Comment on "Ward identities for transport of classical waves in disordered media"

Recently Nieh et al. [Phys. Rev. E 57, 1145 (1998)] have considered a version of derivation of the Ward identities for scalar and vector classical wave field propagation in random media and noted that their results are in contradiction with those obtained by Barabanenkov and Ozrin [Phys. Lett. A 154, 38 (1991)]. In this Comment we show that the derivation given by Nieh et al. is based on an incorrect equation for the energy-vertex function where the term that takes into account the contributions of the scatterer polarization to the field energy is lost. Restoring this term removes the above-noted contradiction.