Comment on "Ward identities for transport of classical waves in disorderedmedia" - art. no. 018601

Recently Nieh et al. [Phys. Rev. E 57, 1145 (1998)] have considered a versi on of derivation of the Ward identities for scalar and vector classical wav e field propagation in random media and noted that their results are in con tradiction 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 polariz ation to the field energy is lost. Restoring this term removes the above-no ted contradiction.