Light-Front QCD: A Constituent Picture of Hadrons

TL;DR

This paper develops a light-front Hamiltonian approach to QCD, introducing a new renormalization method that accounts for symmetry violations and yields a natural confinement mechanism and realistic heavy quark bound states.

Contribution

It introduces a similarity transformation and coupling coherence framework for renormalizing light-front QCD, enabling a constituent picture and confinement insights.

Findings

Correct bound state results in QED using the new Hamiltonian.

Emergence of a simple confinement mechanism in QCD.

Reasonable description of heavy quark bound states.

Abstract

Light-front coordinates offer a scenario in which a constituent approximation of hadron structure can emerge from QCD. This requires cutoffs that violate Lorentz covariance and gauge invariance, and a new renormalization group formalism based on a similarity transformation is used with coupling coherence to fix counterterms that restore these symmetries. The counterterms contain functions of longitudinal momentum fractions which severely complicate renormalization, but they also offer possible resolutions of apparent contradictions between the constituent picture and QCD. The similarity transformation and coupling coherence are applied to QED; and it is shown that the resultant Hamiltonian leads to the correct bound state results. The same techniques are applied to QCD and it is shown that a simple confinement mechanism and a reasonable description of heavy quark bound states emerge naturally.