Abstract
Light-front quantized quark and gluon states (partons) play a dominant role in high energy scattering processes. Initial state hadrons are mixed ensembles of partons, while produced pure partonic states appear as mixed ensembles of hadrons. The transition from collinear hard physics to the 3D structure including partonic transverse momenta is related to confinement which links color and spatial degrees of freedom. We outline ideas on emergent symmetries in the Standard Model and their connection to the 3D structure of hadrons. Wilson loops, including those with light-like Wilson lines such as used in the studies of transverse momentum dependent distribution functions may play a crucial role here, establishing a direct link between transverse spatial degrees of freedom and gluonic degrees of freedom.
Highlights
Quantum chromodynamics (QCD) appears to be a distinct part of the Standard Model describing the strong interactions decoupled from the electroweak interactions
On the other hand the color degree of freedom is clearly visible in the notions of valence quarks and in color factors Nc or 1/Nc in electron–positron annihilation or Drell–Yan scattering, respectively. It is visible in the factorization of high energy scattering processes in distribution functions fH→q and fragmentation functions D(q → h) interpretable as momentum densities of partons q in hadrons H and produced number of hadrons h from parton i, where the interactions of parton(s) i are described within the Standard Model
We have discussed a different view on the emergence of symmetries and asymptotic degrees of freedom in the Standard Model, even if there are still many open ends
Summary
Quantum chromodynamics (QCD) appears to be a distinct part of the Standard Model describing the strong interactions decoupled from the electroweak interactions. On the other hand the color degree of freedom is clearly visible in the notions of valence quarks and in color factors Nc or 1/Nc in electron–positron annihilation or Drell–Yan scattering, respectively It is visible in the factorization of high energy scattering processes in distribution functions fH→q and fragmentation functions D(q → h) interpretable as momentum densities of partons q in hadrons H and produced number of hadrons h from parton i, where the interactions of parton(s) i are described within the Standard Model. As long as the kinematics of the hard process is such that the dependence on one of the light-like components of the partons is power suppressed, there are possibilities to separate the hadronic (soft)
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