The confinement mechanism in the nonperturbative QCD is studied in terms of topological excitation as QCDmonopoles and instantons. In the ’t Hooft abelian gauge, QCD is reduced into an abelian gauge theory with monopoles, and the QCD vacuum can be regarded as the dual superconductor with monopole condensation, which leads to the dual Higgs mechanism. The monopole-current theory extracted from Q...

I review the current status of lattice calculations of heavy quark quantities. Particular emphasis is placed on leptonic and semileptonic decay matrix elements.

We report on our results about hadronic tt̄ production at NLO QCD including t, t̄ spin effects, especially on tt̄ spin correlations.

We review the status of an ongoing long-term lattice investigation of the spectrum and structure of tetraquark candidates. We focus on the light scalar meson a0(980). First steps regarding the study of a possibly existing ccc̄c̄ tetraquark are also outlined.