Quantum Chromodynamics and Parity-Violating Nucleon-Nucleon-Pion Coupling

Abstract

Parity-violating (PV) nucleon-nucleon-pion (NNπ) coupling is studied in order to extract information about nonleptonic weak processes in general. The connection between the PV NNπ amplitude and PV nonleptonic hyperon decays is explored in detail. An outline of the historical background is given. It is shown how the PV NNπ amplitude is to be calculated starting from the Weinberg-Salam model for weak interactions. The effective weak Hamiltonian for PV nonleptonic processes is derived in detail, introducing quantum chromodynamics and flavor-symmetry breaking. The role of the so-called penguin terms is clarified. The PV NNπ amplitude is calculated using current algebra, chiral invariance, and quark models (e.g. the MIT bag model) for the description of baryons. It is emphasized that certain techniques used in the description of nonleptonic decays can undergo an independent test via the study of PV NNπ amplitudes. These amplitudes can be experimentally explored in experiments on nuclear parity violation. A discussion of nuclear calculations and experiments is also included.