A framework for second-order parton showers

A framework is presented for including second-order perturbative corrections to the radiation patterns of parton showers. The formalism allows to combine O(αs2)-corrected iterated 2→3 kernels for “ordered” gluon emissions with tree-level 2→4 kernels for “unordered” ones. The combined Sudakov evolution kernel is thus accurate to O(αs2). As a first step towards a full-fledged implementation of these ideas, we develop an explicit implementation of 2→4 shower branchings in this letter.