Phenomenology of Large N_c QCD

Abstract

These lectures are designed to introduce the methods and results of large N_c QCD in a presentation intended for nuclear and particle physicists alike. Beginning with definitions and motivations of the approach, we demonstrate that all quark and gluon Feynman diagrams are organized into classes based on powers of 1/N_c. We then show that this result can be translated into definite statements about mesons and baryons containing arbitrary numbers of constituents. In the mesons, numerous well-known phenomenological properties follow as immediate consequences of simply counting powers of N_c, while for the baryons, quantitative large N_c analyses of masses and other properties are seen to agree with experiment, even when ``large'' N_c is set equal to its observed value of 3. Large N_c reasoning is also used to explain some simple features of nuclear interactions.