  We study three quark systems in Maximally Abelian (MA) and Maximal Center
(MC) projected QCD on quenched SU(3) lattice, and also in the monopole/photon
part, where only the color-electric/magnetic current exists, using the Hodge
decomposition. First, we perform the quantitative study of the three-quark (3Q)
potential V_{3Q} and the string tension \sigma_{3Q} in baryons. For MA
projected QCD, the monopole part and MC projected QCD, we find that the
confinement potential in V_{3Q} obeys the Y-Ansatz and the string tension
\sigma_{3Q} is approximately equal to that in SU(3) QCD. The universality of
the string tension, \sigma_{3Q} \simeq \sigma_{Q\bar Q}, is also found between
the 3Q and the Q\bar Q potentials. We find a strong similarity of the
inter-quark potential between the monopole part and MC projected QCD. In
contrast, almost no confinement force is found in the inter-quark potential in
the photon part. Next, we study the spectrum of light hadrons in MA projected
QCD and the monopole/photon part, paying attention to the N-\Delta mass
splitting. We find that the N-\Delta mass splitting is significantly reduced in
MA projected QCD and the monopole part, where the one-gluon-exchange effect or
the Coulomb-potential part is largely reduced due to the Abelianization or the
Hodge decomposition. This fact seems to indicate that the main origin of the
mass splitting is one-gluon exchange.
