Possible new species of quarks and hadrons

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Abstract
Assuming that the strong interactions are mediated by a color-SU(3) gauge theory, we consider unusual possibilities for the constituents. The simplest possibility, "shiny" quarks, is that some new quarks are not triplets under color. We analyze the production and signatures for this possibility. Special attention is drawn to the spectroscopy of hadrons containing shiny quarks, some of which are absolutely stable. A more complicated (and possibly deeper dynamically) idea is that of "echo" quarks. These result when the unbroken color SU(3) arises from the breakdown of a larger SU(3) × SU(3) gauge symmetry. The dynamical motivations for this speculation and the distinctive phenomena that follow from it are analyzed. We find that there is no evidence against echo quarks of quite low mass (≳ 2 GeV), which might be produced at present-day accelerators.