Supersymmetric quenching of the Toda lattice equation

The average of the ratio of powers of the spectral determinants of the Dirac operator in the ε-regime of QCD is shown to satisfy a Toda lattice equation. The quenched limit of this Toda lattice equation is obtained using the supersymmetric method. This supersymmetric approach is then shown to be equivalent to taking the replica limit of the Toda lattice equation. Among others, the factorization of the microscopic spectral correlation functions of the QCD Dirac operator into fermionic and bosonic partition functions follows naturally from both approaches. While the replica approach relies on an analytic continuation in the number of flavors no such assumptions are made in the present approach where the numbers of flavors in the Toda lattice equation are strictly integer.