Imaginary chemical potential and finite fermion density on the lattice

Standard lattice fermion algorithms run into the well-known sign problem with a real chemical potential. In this paper we investigate the possibility of using an imaginary chemical potential and argue that it has advantages over other methods, particularly for probing the physics at finite temperature as well as density. As a feasibility study, we present numerical results for the partition function of the two-dimensional Hubbard model with an imaginary chemical potential. We also note that systems with a net imbalance of isospin may be simulated using a real chemical potential that couples to $I_3$ without suffering from the sign problem.