Vortex structure vs. monopole dominance in abelian-projected gauge theory

We find that Polyakov lines, computed in abelian-projected SU(2) lattice ga uge theory in the confined phase, have finite expectation values for lines corresponding to two units of the abelian electric charge. This means that even multiples of abelian electric charge are unconfined, and that the abel ian-projected lattice has at most Z(2), rather than U(1), global symmetry. We also find a severe breakdown of the monopole dominance approximation, as well as positivity, in this charge-2 case. Our results on global Z(2) symm etry contradict both the dual-superconductor and monopole Coulomb gas pictu res of confinement, where all multiples of abelian electric charge (suitabl y identified in an abelian-projection gauge), should be confined. The break down of monopole dominance is also incompatible with a monopole Coulomb gas . Our data is, however, consistent with a center vortex vacuum structure. F urther evidence is provided, in lattice Monte Carlo simulations, for collim ation of confining color-magnetic flux into vortices.