A disorder parameter that tests for confinement in gauge theories with quark fields

We propose to use a suitably defined vortex free energy as a disorder parameter in gauge field theories with matter fields. It is supposed to distinguish between confinement phase, massless phase(s) and Higgs phase where they exist. The matter fields may transform according to an arbitrary representation of the gauge group. We compute the vortex free energy by series expansion for a Z2 Higgs model and for SU (2) lattice models with quark or Higgs fields in the fundamental representation at strong coupling (confinement phase), and for the Z2 Higgs model in the range of validity of low temperature expansions (Higgs phase). The results are in agreement with the expected behaviour. (orig.)