Study of non-perturbative effects of gauge theories using numerical methods

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Abelian mechanism of color confinement is observed bu Suzuki et al. in a gauge-independent way in SU (2) gluodynamics. A new noise-reduction method using random gauge transformations as well as the multi-level method are adopted. A static potential derived from Abelian Polyakov loop correlators gives us the correct string tension. Moreover only the monopole part in the Abelian Polyakov loop is responsible for the string tension. Abelian electric fields defined in an arbitrary color direction are squeezed and the corresponding monopole currents play the role of magnetic super currents. The penetration and the coherence lengths are consistent with those observed previously after Abelian projections. Since an Abelian neutral state in all color channels is restricted to a color-singlet state alone, the non-Abelian color confinement in SU (2) gluodynamics can be understood as the Abelian dual Meissner effect due to monopoles.Kubo found that a certain flavor symmetry based on a non-abelian discrete group can be realized at low energies. Discrete flavor symmetries can originate from the geometry of compactified extra dimensions. They make predictions that can be tested by future experiments such as Large Hadron Colider experiments and Super B-Factory experiments at KEK.The running coupling and the Kugo-Ojima confinement parameter were analyzed by Nakajima and his colaborator in lattice Landau gauge QCD with use of quenched and unquenched gauge configurations. Although the running coupling measured by the ghost and gluon dressing function is infrared suppressed, the running coupling has a maximum of $\alpha_0\sim 2-2.5$ at around $q=0.5$ GeV irrespective of the fermion actions (Wilson fermions and Kogut-Susskind fermions). The Kugo-Ojima Parameter $c$ which saturates to about 0.8 in quenched simulations becomes consistent with the expected value, 1, in the MILC configurations produced with the use of Asqtad action.