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Open issues in confinement, for the lattice and for center vortices

Topological confinement by center vortices does not immediately explain either a minimum-area law for non-planar Wilson loops or the Lüscher term. I conjecture that both a minimal-area law and a Lüscher term arise in a confinement model of random ensembles of vortices with no propagating gluons (a polymer model), and propose their test by polymer-like lattice simulations. I also consider the role of dynamically-massive gluons propagating from one point to another on a Wilson loop, and conjecture an approximate duality between the gluon-chain model and a condensate of center vortices with nexuses (magnetic monopoles) propagating on the vortex surfaces. I explore the old fishnet model, updated to deal with propagating massive QCD gluons, and argue that it leads to a surface tension and therefore a Lüscher term, as expressed through an effective action of the Dirichlet form that describes tension. I propose various lattice studies of non-planar Wilson loops to investigate such issues. Finally, in a different vein I urge the lattice community to study gauge-fixing to the background-field Feynman gauge, which will yield the gauge-invariant off-shell Greens functions of the pinch technique.