Acceleration of the Arnoldi method and real eigenvalues of the non-Hermitian Wilson–Dirac operator

In this paper, we present a method for the computation of the low-lying real eigenvalues of the Wilson–Dirac operator based on the Arnoldi algorithm. These eigenvalues contain information about several observables. We used them to calculate the sign of the fermion determinant in one-flavor QCD and the sign of the Pfaffian in N = 1 super Yang–Mills theory. The method is based on polynomial transformations of the Wilson–Dirac operator, leading to considerable improvements of the computation of eigenvalues. We introduce an iterative procedure for the construction of the polynomials and demonstrate the improvement in the efficiency of the computation. In general, the method can be applied to operators with a symmetric and bounded eigenspectrum. ► We present a method to compute small real eigenvalues of the Wilson–Dirac operator. ► The method is based on a polynomial acceleration of the Arnoldi algorithm. ► We present an iterative method to construct the polynomials. ► We obtained the reweighting factors in one-flavor QCD and super Yang–Mills theory. ► The method can be applied to operators with a symmetric and bounded eigenspectrum.