Improved lattice actions with chemical potential

We give a prescription how to include a chemical potential μ into a general lattice action. This inclusion does not cause any lattice artifacts. Hence its application to an improved - or even perfect - action at μ=0 yields an improved resp. perfect action at arbitrary μ. For short-ranged improved actions, a good scaling behavior holds over a wide region, and the upper bound for the baryon density - which is known for the standard lattice actions - can be exceeded. (orig.)