BOUNDS ON VERTICAL-BAR-G(M)(N)VERTICAL-BAR/G(M)(P) FROM QCD SUM-RULES

Using the theoretical constraints set by QCD sum rules on the moments of nucleon distribution amplitudes, we derive bounds on the ratio R = \G(M)n\/G(M)p. We find a striking scaling behavior between R and the expansion coefficient B4 of the Appell polynomial decomposition of the nucleon distribution amplitude. Such a scaling law can be used to validate or exclude candidate models, thus shortcutting explicit calculations. The implications for elastic nucleon cross sections are examined.