1. Trace anomalies and the Hawking effect;Christensen;King's College preprint,1976
2. S.L. Adler, J. Liebermann and Y.J. Ng, Regularization of the stress-energy tensor for vector and scalar particles propagating in a general background metric, Institute for Advanced Study preprint COO-2220-83. The method employed here seems extremely likely to yield a vanishing trace for fermions also.
3. Trace anomalies in dimensional regularization
4. Non-local conformal anomalies;Deser;King's College Preprint,1976