Two Topics in Quantum Chromodynamics

Abstract

Quantum chromodynamics (QCD) has reached a level of credibility and maturity which deserves textbook status. Indeed, textbooks exist1 and others are on the way.2 Nevertheless, to my mind a textbook treatment of QCD is made much more difficult than that of quantum electrodynamics (QED) because of the confinement problem. Even perturbative QCD—which is all that will really be discussed here—suffers this problem. There is no S-matrix theory of quarks and gluons as there is for QED, as given in the LSZ formalism.3 The concept of “on-mass-shell” or “asymptotic” quark and/or gluon is highly suspect. And the typical “Feynman diagram” used in perturbative QCD contains internal quark and gluon lines and external hadron lines. What does that really mean? How does one derive and justify Feynman-rules for such amplitudes in the absence of good control over the confinement question?KeywordsStructure FunctionQuantum Chromo DynamicPerturbation SeriesAbsorptive PartCurrent Correlation FunctionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.