Low-Energy Strong Interactions

Abstract

Because the strong-interaction coupling constants are so large, a perturbation theory of lowest-order strong-interaction Feynman diagrams does not always make sense. Yet if interpreted in the right manner (i.e., at low energies), such graphs reveal a great deal about the qualitative and sometimes quantitative nature of hadron (strong-interaction) physics. They are also the beginnings of the dynamical scheme of strong-interaction dispersion theory, a theory that we will pursue in greater detail in Chapter 15. Here we begin by investigating the basic pion-exchange, short-range Yukawa force. Next we develop the concept of isospin, isospin conservation, and isospin projection operators, which we fold into the Feynman rules. Then we use simple Feynman graphs to explain the essential features of the long-range part of the nucleon-nucleon force, and low-energy scattering. Feynman graphs are also used to explain low-energy pion-nucleon scattering and the dynamical effect of the 33 resonance, Δ(1232). Finally, we search for conserved and approximately conserved currents for hadronic interactions. Conserved isotopic vector currents are investigated in the context of the vector-meson dominance model, and partially conserved, isotopic axial-vector currents are probed in the context of pion pole dominance.