IV.R338 — Structural origin of the exponent 7

The evaluation point s = 4 is forced by the mass operator (B raised to the fourth power yields mass via the trace formula); the exponent 7 = 2*4-1 counts total independent oscillation directions in the fibered product: dim(tau^3)+dim(T^2)+dim(tau^1)+1 = 3+2+1+1 = 7.