Covariant perturbation theory III. Spectral representations (Nucl.Phys.B 333)
Barvinsky, Vilkovisky.
Extension of covariant perturbation theory to third order in curvature requires the triple- spectral forms for one-loop vertex functions of massless fields to be established. For the simplest triangular graph with unit vertices the three spectral masses are known to form a triangle, and the spectral weight is 1/4πS where S is the area of this triangle. We generalize this result to an arbitrary derivative coupling.
