Monopoles in QCD

Based on the dual Higgs picture for confinement, we study monopole properties in the maximally abelian (MA) gauge using the lattice QCD. The monopole carries a large fluctuation of the gluon field and provides a large abelian action in abelian projected QCD (AP-QCD). We find large cancellation between abelian part and off-diagonal part of the action density around the monopole, which ensures the appearance of monopoles. The monopole in the MA gauge can be regarded as the collective mode of the large gluon fluctuation concentrated into the abelian sector, and would be relevant degrees of freedom for confinement in AP-QCD.