Remarks on diquarks, strong binding, and a large hidden QCD scale

We present arguments regarding the possible role of diquarks in low-energy hadron phenomenology that has so far escaped theorists' attention. Good diquarks, i.e. the 0(+) states of two quarks, are argued to have a two-component structure with one of the components peaking at distances several times shorter than a typical hadron size (a short-range core). This can play a role in solving two old puzzles of the 't Hooft 1/N expansion: strong quark-mass dependence of vacuum energy density and strong violations of the Okubo-Zweig-Iizuka (OZI) rule in quark-antiquark 0(+/-) channels. In both cases empiric data defy 't Hooft's 1/N suppression. If good diquarks play a role at an intermediate energy scale they ruin 't Hooft's planarity because of their mixed-flavor composition. This new scale associated with good diquarks may be related to a numerically large scale discovered in [V. A. Novikov, M. A. Shifman, A. I. Vainshtein, and V. I. Zakharov, Nucl. Phys. B 191, 301 (1981)] in a number of phenomena mostly related to vacuum quantum numbers and 0(+/-) glueball channels. If SU(3)(color) of bona fide QCD is replaced by SU(2)(color), diquarks become well-defined gauge-invariant objects. Moreover, there is an exact symmetry relating them to pions. In this limit predictions regarding good diquarks are ironclad. If passage from SU(2)(color) to SU(3)(color) does not lead to dramatic disturbances, these predictions remain qualitatively valid in bona fide QCD.