Truncated determinant approach to light dynamical quarks

Virtual quark effects in lattice QCD are studied in an approach where the i nfrared modes are included in a. precise and gauge-invariant manner, Bt fix ed physical volume the required number of modes does not increase in the co ntinuum limit! and the acceptance is tolerable even for very light quark ma sses, Topological change distributions at varying quark mass, and the stati c quark potential, showing the onset of string-breaking, are presented in b oth QED2 and QCD4.