On the breaking of collinear factorization in QCD

TL;DR

This paper analyzes the failure of collinear factorization in QCD for non-inclusive observables, revealing violations at high loop levels due to complex gluon exchange interactions, with implications for understanding QCD processes.

Contribution

It identifies the specific conditions and loop levels at which collinear factorization breaks down in QCD and related theories, highlighting the role of gluon exchanges and phase differences.

Findings

Factorization is violated at three-loop level in pure QCD.

Violation driven by non-commuting Coulomb/Glauber gluons.

Potential violations at two-loop level in theories beyond QCD.

Abstract

We investigate the breakdown of collinear factorization for non-inclusive observables in hadron-hadron collisions. For pure QCD processes, factorization is violated at the three-loop level and it has a structure identical to that encountered previously in the case of super-leading logarithms. In particular, it is driven by the non-commutation of Coulomb/Glauber gluon exchanges with other soft exchanges. Beyond QCD, factorization may be violated at the two-loop level provided that the hard subprocess contains matrix element contributions with phase differences between different colour topologies.