Abstract
Abstract For many practical purposes, it is convenient to formulate unbroken non-abelian gauge theories like QCD in a color-flow basis. We present a new derivation of SU(N) interactions in the color-flow basis by extending the gauge group to U(N) × U(1)′ in such a way that the two U(1) factors cancel each other. We use the quantum action principles to show the equivalence to the usual basis to all orders in perturbation theory. We extend the known Feynman rules to exotic color representations (e.g. sextets) and discuss practical applications as they occur in automatic computation programs.
Highlights
The analysis of particle physics experiments at colliders depends on reliable theoretical predictions for cross sections of scattering processes
The expansion of QCD amplitudes in a color-flow basis has been known as a useful device in various contexts of perturbative and non-perturbative calculations
We have demonstrated that it can be understood as a field theory of its own, a priori different from, but equivalent to, standard QCD
Summary
The analysis of particle physics experiments at colliders depends on reliable theoretical predictions for cross sections of scattering processes. The derivation [18] of the color-flow representation is incomplete in two directions: firstly, there is no consideration of interactions with more exotic color structures, in particular beyond QCD with fermionic matter in the fundamental representation, and secondly the discussion is deliberately confined to tree level amplitudes These two limitations are related, and overcoming them is of theoretical interest: the most important light Higgs production channel at LHC involves the dimension-5 operator H Tr (FμνF μν), which arises from a loop and corresponds to an octet-octet-singlet coupling that cannot be described straightforwardly in the framework provided by [18]. As an example of exotic color representations, we extend those rules to color-sextet particles in appendix B
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