Exact Chiral Invariance at Finite Density on Lattice
  A new lattice action is proposed for the overlap Dirac matrix with nonzero chemical potential. It is shown to preserve the full chiral invariance for all values of lattice spacing exactly. It is further demonstrated to arise in the domain wall formalism by coupling the chemical potential count only to the physically relevant wall modes. 
Rajiv V. Gavai and Sayantan Sharma
hep-lat