  Green functions in a quantum field theory can be expanded as bivariate series
in the coupling and a scale parameter. The leading logs are given by the main
diagonal of this expansion, i.e. the subseries where the coupling and the scale
parameter appear to the same power; then the next-to leading logs are listed by
the next diagonal of the expansion, where the power of the coupling is
incremented by one, and so on. We give a general method for deriving explicit
formulas and asymptotic estimates for any next-to$^k$ leading-log expansion for
a large class of single scale Green functions. These Green functions are
solutions to Dyson-Schwinger equations that are known by previous work to be
expressible in terms of chord diagrams. We look in detail at the Green function
for the fermion propagator in massless Yukawa theory as one example, and the
Green function of the photon propagator in quantum electrodynamics as a second
example, as well as giving general theorems. Our methods are combinatorial, but
the consequences are physical, giving information on which terms dominate and
on the dichotomy between gauge theories and other quantum field theories.
