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 μ_{B} \neq 0 provided one adds appropriate deformation terms to the SO(2N_{c}) theory. This opens up the prospect of learning about QCD at μ_{B} \neq 0 using lattice studies of the SO(2N_{c}) theory.