Trace anomaly of the stress-energy tensor for massless vector particles propagating in a general background metric

We reanalyze the problem of regularization of the stress-energy tensor for massless vector particles propagating in a general background metric, using covariant point separation techniques applied to the Hadamard elementary solution. We correct an error, pointed out by Wald, in the earlier formulation of Adler, Lieberman, and Ng, and find a stress-energy tensor trace anomaly agreeing with that found by other regularization methods.