The Rapidity Renormalization Group
  We introduce a systematic approach for the resummation of perturbative series which involve large logarithms not only due to large invariant mass ratios but large rapidities as well. Series of this form can appear in a variety of gauge theory observables. The formalism is utilized to calculate the jet broadening event shape in a systematic fashion to next to leading logarithmic order. An operator definition of the factorized cross section as well as a closed form of the next-to leading log cross section are presented. The result agrees with the data to within errors. 
Jui-yu Chiu, Ambar Jain, Duff Neill, Ira Z. Rothstein
hep-ph hep-th nucl-th