Calorons, instantons, and constituent monopoles in SU(3) lattice gauge theory

We analyze the zero modes of the Dirac operator in quenched SU(3) gauge configurations at a nonzero temperature and compare periodic and anti-periodic temporal boundary conditions for the fermions. It is demonstrated that for the different boundary conditions often the modes are localized at different space-time points and have different sizes. Our observations are consistent with patterns expected for Kraan-van Baal solutions of the classical Yang-Mills equations. These solutions consist of constituent monopoles and the zero modes are localized on different constituents for different boundary conditions. Our findings indicate that the excitations of the QCD vacuum are more structured than simple instantonlike lumps.