Third Order Lagrangians, Weyl Invariants & Classical Trace Anomaly in   Six Dimensions
  We have proceeded analogy of Einstein tensor and alternative form of Einstein field equations for generic coeffcients of eight terms in third order of Lovelock Lagrangian. We have found constraint between the coeffcients into two forms, an independent and a dimensional dependent versions. Each form has three degrees of freedom, and not only the exact coeffcients of third order Lovelock Lagrangian satisfy the two forms of constraints, also the two independent cubic of Weyl tensor satisfy the independent constraint in six dimensions and yield the dimensional dependent version identically independent of dimension. We have introduced most general effective expression for a total third order type Lagrangian with the homogeneity degree number three which includes the previous eight terms plus new three ones among all seventeen independent terms. We have proceeded analogy for this combination, and have achieved relevant constraint. We have shown that expressions given in literature as third Weyl invariant combination in six dimensions satisfy this constraint. Thus, we suggest that these constraint relations to be considered as the necessary consistency conditions on the numerical coeffcients that a Weyl invariant in six dimensions should satisfy. We have calculated the "classical" trace anomaly (an approach that was presented in our previous works) for introduced total third order type Lagrangian and have achieved general expression with four degrees of freedom in more than six dimensions. We have demonstrated that resulted expression contains exactly relevant coeffcient of Schwinger-DeWitt proper time method (linked with relevant heat kernel coeffcient) in six dimensions, as a particular case. Our approach can be regarded as alternative derivation of trace anomaly which also gives general expression with the relevant degrees of freedom. 
Mehrdad Farhoudi
gr-qc hep-th math-ph math.MP