Embedding the Standard Model symmetry group in higher-dimensional theories often results in additional gauge groups at low-energy that have observable consequences at collider experiments. One such extension that appears in some string inspired models and supersymmetric scenarios is an additional SU(N) with fundamental fermions similar to the quarks of QCD. However, If the confinement scale of the interaction is smaller than the mass of the fundamental fermions, string breaking by spontaneous production of fermion-antifermion pairs as in the familiar jet fragmentation of QCD, is exponentially suppressed. In this case, the fermions are called quirks, and the analog to QCD color charge for the quirks is called infracolor.
The key model parameters are the mass of the lightest quirk and the confinement scale, and the range in these parameters not constrained by existing data or cosmological considerations is large, resulting in a broad range of phenomenologies, many of which have very unusual signatures for observation.