General bounds on the Wilson-Dirac operator

Lower bounds on the magnitude of the spectrum of the Hermitian WilsonDirac operator H(m) have previously been derived for 0 < m < 2 when the lattice gauge field satisfies a certain smoothness condition. In this paper lower bounds are derived for 2p−2 < m < 2p for general p = 1, 2, . . . , d where d is the spacetime dimension. The bounds can alternatively be viewed as localisation bounds on the real spectrum of the usual Wilson-Dirac operator. They are needed for the rigorous evaluation of the classical continuum limit of the axial anomaly and index of the overlap Dirac operator at general values of m, and provide information on the topological phase structure of overlap fermions. They are also useful for understanding the instanton size-dependence of the real spectrum of the Wilson-Dirac operator in an instanton background.