Lower excitation spectrum of the nucleon and delta in a relativistic chiral quark model

The lower excitation spectrum of the nucleon and Δ 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. The obtained structure of one-meson exchange interaction confirms a prediction of the large Nc limit approach stating that the mass splitting between various baryon states receives contributions from operators which simultaneously couple spin, isospin and orbital momentum. It is shown that one-meson exchange interaction generates a splitting between negative parity N*(1/2-) and N*(3/2-) states, and also between Δ*(3/2-) and Δ*(1/2-) states in contrast to the non-relativistic Goldstone boson exchange based quark models