Colour Evolution and Infrared Physics

Abstract

We give a complete account of how soft gluon, massless quark, evolution equations in colour space originate, from a factorization into a hard cross section density operator and a soft function encoding measurements and the projection on definite colours. We detail this formalism up to the two loop level and we demonstrate how the evolution kernels relate to infrared subtractions, and how the resolution of infrared singular regions conspires with the structure of observables the algorithm should be able to predict. The latter allows us to address evolution in different kinematic variables, including energy ordering and angular cutoffs in non-global observables. The soft factor and its evolution resembles a hadronization model including effects such as colour reconnection, and could give insight into the structure of power corrections in observables which require soft gluon evolution.

31 pages, 2 figures, significantly extended with additional appendices and outlook, corresponds to version accepted by JHEP

References in corpus (10)

• Herwig++ Physics and Manual
• Designing Gapped Soft Functions for Jet Production
• Numerical NLO QCD calculations
• Higher-order non-global logarithms from jet calculus
• Resummation of Super-Leading Logarithms
• Two-loop anomalous dimension for the resummation of non-global observables
• Coulomb gluons will generally destroy coherence
• Double parton distributions out of bounds in colour space
• Multivariable evolution in final state parton shower algorithms
• Multivariable evolution in parton showers with initial state partons

Cited by in corpus (3)

• Wigner 6j symbols for SU(N): Symbols with at least two quark-lines
• Wigner 6j symbols with gluon lines: completing the set of 6j symbols required for color decomposition
• Dark Sector Showers and Hadronisation in Herwig 7