Lower Excitation Spectrum of the Nucleon and Delta in a Relativistic Chiral Quark Model
Annotatsiya
The lower excitation spectrum of the nucleon and $\\Delta$ is calculated in a relativistic chiral quark model. Contributions of the second order self-energy and exchange diagrams due-to pion fields to the mass spectrum of the SU(2) baryons are estimated. A splitting between N(939) and positive parity nucleon resonance (Roper resonance) $N^*(1440)$ is reproduced with a reasonable accuracy. It is shown that the relativistic structure of the one-meson exchange interaction yields a splitting between negative parity $N^*(1/2^-)$ and $N^*(3/2^-)$ states, and also between $\\Delta^*(3/2^-)$ and $\\Delta^*(1/2^-)$ states in contrast to the non-relativistic Goldstone-Boson Exchange based quark models. This splitting is due-to a relativistic operator which couples the lower and upper orbital momentum of two interacting valence quarks.