Orbifold equivalence and the sign problem at finite Baryon density

We point out that SO(2N_c) gauge theory with N_f fundamental Dirac fermions does not have a sign problem at finite baryon number chemical potential μ_B. One can thus use lattice Monte Carlo simulations to study this theory at finite density. The absence of a sign problem in the SO(2N_c) theory is particularly interesting because a wide class of observables in the SO(2N_c) theory coincide with observables in QCD in the large N_c limit, as we show using the technique of large N_c orbifold equivalence. We argue that the orbifold equivalence between the two theories continues to hold at finite μ_B provided one adds appropriate deformation terms to the SO(2N_c) theory. This opens up the prospect of learning about QCD at finite μ_B using lattice studies of the SO(2N_c) theory.