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. For this reason, simple extensions to the Standard Model group are always promising candidates for new physics independent of specific models. One simple extension is an additional SU(N) with fundamental fermions similar to the quarks of QCD. If the interaction is QCD-like, generic searches for new massive quarks and stable massive particles are likely to have some sensitivity.
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, called "quirks", are bound in pairs by "infracolor" strings. The large range of quirk masses and infracolor confinement scales allowed by previous measurements and cosmological constraints results in widely varied and rather bizarre phenomenologies that present unusual challenges for detection.