  As a topic of "quantum color dynamics", we study various mass generation of
colored particles and gluonic dressing effect in a non-perturbative manner,
using the Schwinger-Dyson (SD) formalism in (scalar) QCD. First, we review
dynamical quark-mass generation in QCD in the SD approach as a typical
fermion-mass generation via spontaneous chiral-symmetry breaking. Second, using
the SD formalism for scalar QCD, we investigate the scalar diquark, a
bound-state-like object of two quarks, and its mass generation, which is
clearly non-chiral-origin. Here, the scalar diquark is treated as an extended
colored scalar field, like a meson in effective hadron models, and its
effective size $R$ is introduced as a form factor. As a diagrammatical
difference, the SD equation for the scalar diquark has an additional 4-point
interaction term, in comparison with the single quark case. The diquark size
$R$ is taken to be smaller than a hadron, $R\sim 1$ fm, and larger than a
constituent quark, $R\sim 0.3$ fm. We find that the compact diquark with
$R\simeq 0.3$ fm has a large effective mass of about 900 MeV, and therefore
such a compact diquark is not acceptable in effective models for hadrons. We
also consider the artificial removal of 3- and 4-point interaction,
respectively, to see the role of each term, and find that the 4-point
interaction plays the dominant role of the diquark self-energy. From the above
two different cases, quarks and diquarks, we guess that the mass generation of
colored particles is a general result of non-perturbative gluonic dressing
effect.
