The Feynman-Schwinger (world-line) representation in perturbative QCD
  The proper time path integral representation is derived explicitly for an arbitrary $n$-point amplitude in QCD. In the standard perturbation theory the formalism allows to sum up the leading subseries, e.g. yielding double-logarithm Sudakov asymptotics for form factors. Correspondence with the standard perturbation theory is established and connection to the Bern-Kosower-Strassler method is illustrated. 
Yu.A.Simonov (Jefferson Lab, Newport News, USA and ITEP, Moscow,   Russia) and J.A.Tjon (U. Utrecht and Groningen, The Nethe...