Baryon distribution amplitudes in QCD

We develop a new theoretical framework for the description of leading twist light-cone baryon distribution amplitudes which is based on integrability of the helicity lambda = 3/2 evolution equation to leading logarithmic accuracy. A physical interpretation is that one can identify a new 'hidden' quantum number which distinguishes components in the A = 3/2 distribution amplitudes with different scale dependence. The solution of the corresponding evolution equation is reduced to a simple three-term recurrence relation. The exact analytic solution is found for the component with the lowest anomalous dimension for all moments N, and the WKB-type expansion is constructed for other levels, which becomes asymptotically exact at large N. Evolution equations for the lambda = 1/2 distribution amplitudes (e.g. for the nucleon) are studied as well, We find that the two lowest anomalous dimensions for the lambda = 1/2 operators (one for each parity) are separated from the rest of the spectrum by a finite 'mass gap', These special states can be interpreted as scalar diquarks. (C) 1999 Elsevier Science B.V. All rights reserved.