Phenomenological bridge between high- and low-energy behavior in QCD

So far, permanent confinement of quarks is a purely phenomenological principle, not yet derived from quantum chromodynamics (QCD). A phenomenological model is exhibited that has confinement as well as the usual asymptotically-free short-distance behavior of QCD, and a crude approximation is made to the so-called energy-momentum sum rule of deep inelastic lepton-proton scattering, yielding about 0.65 as the quark energy fraction at |k2| ⋍ 3−4 GeV2.