PERFECT ACTIONS WITH CHEMICAL-POTENTIAL

We show how to include a chemical potential mu in perfect lattice acti ons, It turns out that the standard procedure of multiplying the quark fields Psi, <(Psi)over bar> at Euclidean time t by exp(+ mu t), respe ctively, is perfect. As an example, the case of free fermions with che mical potential is worked out explicitly. Even after truncation, cut-o ff effects in the pressure and the baryon density are small. Using a ( quasi-)perfect action, numerical QCD simulations for non-zero chemical potential become more powerful, because coarse lattices are sufficien t for extracting continuum physics. (C) 1998 Elsevier Science B.V. All rights reserved.