Diquarks as Inspiration and as Objects

Abstract

It is plausible that several of the most profound aspects of low-energy QCD dynamics are connected to diquark correlations, including: paucity of exotics (which is the foundation of the quark model and of traditional nuclear physics), similarity of mesons and baryons, color superconductivity at high density, hyperfine splittings, $\Delta I=1/2$ rule, and some striking features of structure and fragmentation functions. After a brief overview of these issues, I discuss how diquarks can be studied in isolation, both phenomenologically and numerically, and present approximate mass differences for diquarks with different quantum numbers. The mass-loaded generalization of the Chew-Frautschi formula provides an essential tool.

15 pages, 1 figure. Solicited contribution to the Ian Kogan memorial volume, ed. M. Shifman. v2: several typos corrected

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