\(\hbox {Next-to}{}^k\) Leading Log Expansions by Chord Diagrams


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 \(\hbox {next-to}{}^k\) 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.

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    Here primitive means primitive in the renormalization Hopf algebra, or equivalently having no proper subdivergences.

  2. 2.

    Note that because of an unfortunate sign convention originating in [18] and carried throughout related work, the sign of L is opposite to what would be in most of the physics literature, and so it is perhaps best to view L as \(-\log (q^2/\mu ^2)\). In particular this leads to a sign difference in the comparison with the work of Krüger and Kreimer in Sect. 6.1.

  3. 3.

    An analysis not working in a quotient algebra should also be possible but would involve machinery similar to that which will be needed for extending the chord diagram expansions to systems of Dyson–Schwinger equations. In both cases this remains work for the future.


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Correspondence to Karen Yeats.

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J.C. is supported by the French INS2I JCJC Grant ASTEC. K.Y. is supported by an NSERC Discovery grant and the Canada Research Chair program. Thanks to the referee for their insightful comments.

Communicated by H. Duminil-Copin

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Courtiel, J., Yeats, K. \(\hbox {Next-to}{}^k\) Leading Log Expansions by Chord Diagrams. Commun. Math. Phys. 377, 469–501 (2020). https://doi.org/10.1007/s00220-020-03691-7

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