Research for Nonperturbative Properties of Quarks, Gluons and Hadrons in Quantum Chromodynamics

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Based on quantum chromodynamics (QCD), the fundamental theory of the strong interaction, we have performed highly original studies on color confinement, quark many-body systems, quark-gluon-plasma (QGP), holographic QCD obtained from the superstring theory, and so on.1. We perform in detail the first accurate lattice-QCD study of the three-quark potential, responsible to the physical properties of baryons such as nucleons. We clarify that the three-quark potential is described by the sum of two-body Coulomb and Y-type linear confinement potential. This study is established as an important work and is cited by Prof. Rothe's textbook "Lattice Gauge Theories".2. We perform the first study of baryons as chiral solitons in holographic QCD, which is obtained from the D-brane system corresponding to QCD using the gauge/gravity duality in the superstring theory.3. We perform in detail the first lattice-QCD study of the confinement potential in the quark many-body systems such as tetra-quarks and penta-quarks, and find that the string picture is applicable even for these quark many-body systems at large-distances.4. We perform in detail the first study of the gluonic excitation in three-quark systems in lattice QCD, and find a large gluonic excitation energy of about 1GeV, which is conjectured to lead to a physical reason of the success of the quark model without gluons.5. We study penta-quark baryons in lattice QCD with checking the boundary-condition dependence, and show that no penta-quark resonance appears below 1.75GeV.6. We study charmonia at finite temperature in lattice QCD with checking the boundary-condition dependence, and find that J/Psi survives as a hadronic resonance even above the critical temperature, i.e., in QGP. 7. We combine the Schwinger-Dyson equation and lattice QCD results, and investigate finite temperature/density QCD.8. We perform the first study of the quark-gluon mixed condensate at finite temperature in lattice QCD.