We study three subjects on quark confinement in hadrons in SU(3)$_{rm c}$ lattice QCD. From the accurate lattice calculation for more than 300 different patterns of three-quark (3Q) systems, we find that the static 3Q potential is well described by Y
-Ansatz, i.e., the Coulomb plus Y-type linear potential. We also study the multi-quark (4Q, 5Q) potentials in lattice QCD, and find that they are well described by the one-gluon-exchange (OGE) Coulomb plus string-theoretical linear potential, which supports the {it infrared string picture} even for the multi-quarks. The second subject is a lattice-QCD determination of the relevant gluonic momentum component for confinement. The string tension (confining force) is found to be almost unchanged even after cutting off the high-momentum gluon component above 1.5GeV in the Landau gauge. In fact, {it quark confinement originates from the low-momentum gluon below about 1.5GeV.} Finally, we consider a possible gauge of QCD for the quark potential model, by investigating instantaneous inter-quark potential in generalized Landau gauge, which describes a continuous change from the Landau gauge to the Coulomb gauge.
We perform the first study for the bound states of colored scalar particles $phi$ (scalar quarks) in terms of mass generation with quenched SU(3)$_c$ lattice QCD. We investigate the bound states of $phi$, $phi^daggerphi$ and $phiphiphi$ (scalar-quark
hadrons), as well as the bound states of $phi$ and quarks $psi$, i.e., $phi^daggerpsi$, $psipsiphi$ and $phiphipsi$ (chimera hadrons). All these new-type hadrons including $phi$ have a large mass of several GeV due to large quantum corrections by gluons, even for zero bare scalar-quark mass $m_phi=0$ at $a^{-1}sim 1{rm GeV}$. We find a similar $m_psi$-dependence between $phi^daggerpsi$ and $phiphipsi$, which indicates their similar structure due to the large mass of $phi$. From this study, we conjecture that all colored particles generally acquire a large effective mass due to dressed gluons.
We study baryons and baryonic matter in holographic QCD using a D4/D8/$bar{rm D8}$ multi-D-brane system in the superstring theory. We obtain the chiral soliton solution for baryons in the four-dimensional meson theory derived from the multi-D-brane s
ystem. For the analysis of finite baryon-density matter, we investigate the chiral soliton on $S^3$ in holographic QCD, and find the delocalization of the soliton, i.e., the swelling of baryons in dense matter.
We perform the first studies of various inter-quark potentials in SU(3)$_{rm c}$ lattice QCD. From the accurate lattice calculation for more than 300 different patterns of three-quark (3Q) systems, we find that the static 3Q potential $V_{rm 3Q}$ is
well described by Y-Ansatz, i.e., the Coulomb plus Y-type linear potential. Quark confinement mechanism in baryons is also investigated in maximally-Abelian projected QCD. We next study the multi-quark potentials $V_{n{rm Q}}$ ($n$=4,5) in SU(3)$_{rm c}$ lattice QCD, and find that they are well described by the one-gluon-exchange Coulomb plus multi-Y type linear potential, which supports the flux-tube picture even for the multi-quarks. Finally, we study the heavy-heavy-light quark (QQq) potential both in lattice QCD and in a lattice-QCD-based quark model.
