2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148899We study $U_A$(1) anomaly of non-perturbative QCD in the maximally abelian gauge on SU(2) lattice. The existence of the strong correlation between QCD-monopoles and instantons in the abelian gauge is shown by both analytic and numerical works including lattice simulations. These results bring us a conjecture that the $U_A$(1) symmetry would be explicitly broken in the background fields dominated by QCD-monopoles. We find an evidence for our conjecture by measuring the chiral-asymmetric zero modes of the Dirac operator in the backgrounds of QCD-monopoles.17 pages, revtex, 19 postscript figures includedHigh Energy Physics - Latticetext