Padé–Z2 stochastic estimator of determinants applied to quark loop expansion of lattice QCD

In lattice QCD calculation, evaluating the fermion determinant is computationally expensive and as a consequence detM is often not evaluated and is simply set equal to a constant. This is called the quenched approximation and amounts to neglecting internal fermion loops. The goal of this work is to study the systematic error introduced by quenching and to compensate for quenching errors by constructing an expansion in quark-loop count and using it to improve Monte Carlo estimators of Wilson loops measured on quenched gauge field configurations. We examine a source of statistical error and a method for its partial alleviation.