Diffeomorphisms, Anomalies and the Fefferman-Graham Ambiguity
  Using the Weyl transfomations induced by diffeomorphisms we set up a cohomological problem for the Fefferman-Graham coefficients. The cohomologically nontrivial solutions remove the ambiguity and give the nonlocal terms in the effective action responsible for the trace anomalies. 
A. Schwimmer and S. Theisen