5. SINGULARITIES IN FEYNMAN GRAPHS 45
Figure 2. The first few expressions in the renormalization
group flow from scale ε to scale L.
Consider the graph γ1, given by
We see that
wγ1 (P (ε, L),I)(a) =
a(x)Kl(x, x)d VolM dl
where d VolM is the volume form associated to the metric on M, and a ∈
is the field we place at the external edge of the graph. Since
l− dim M/2
+ higher order terms
for l small, the limit limε→0 wγ1 (P (ε, L),I)(a) doesn’t exist.