Rapidity Renormalization Group
Observables in QCD are often plagued by large logarithms in certain limits, spoiling the perturbation series. Factorization has been a powerful paradigm to deal with the resummation of these logarithms, and soft-collinear effective field theory provides a good framework to pursue factorization. However the traditional formulation of SCET is insufficient for certain observables, where soft radiation can provide significant recoil to the collinear modes.
Examples include the jet broadening event shape, and the Drell-Yan or Higgs pt spectrum. A different formulation of SCET is necessary, and introduces a new set of divergences associated with the rapidity integrations that are not regulated by standard techniques. With appropriate regularization and subtractions, these divergences can be renormalized, and a systematic, consistent resummation formula produced. Further, the formalism developed can be applied to many different observables, revealing a unity of underlying structure.