  We find that QCD in covariant gauge yields zero for the topological
susceptibility, even at the nonperturbative level. The result is derived in two
ways, one using translational invariance, and the other using the BRST
Hamiltonian. Comparison with the canonical formalism suggests that QCD is not
uniquely defined at the nonperturbative level. Supporting evidence is also
provided in 1+1 dimensions. Our results imply that the strong CP problem admits
a trivial resolution in covariant gauge, but obstacles remain for the U(1)
problem.

High Energy Physics - Theory