Perfect actions with chemical potential

We show how to include a chemical potential μ in perfect lattice actions. It turns out that the standard procedure of multiplying the quark fields Ψ,Ψ̄ at Euclidean time t by exp(±μt), respectively, is perfect. As an example, the case of free fermions with chemical potential is worked out explicitly. Even after truncation, cut-off 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 sufficient for extracting continuum physics.