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The lower excitation spectrum of the nucleon and $\Delta$ is calculated in arelativistic chiral quark model. Contributions of the second order self-energyand 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 nucleonresonance (Roper resonance) $N^*(1440)$ is reproduced with a reasonableaccuracy. The obtained structure of one-meson exchange interaction confirms aprediction of the large $N_c$ limit approach stating that the mass splittingbetween various baryon states receive contributions from operators whichsimultaneously couple spin, isospin and orbital momentum. It is shown thatone-meson exchange interaction generates 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-BosonExchange based quark models. This splitting is due-to a relativistic operatorwhich couples the lower and upper orbital momentum of two interacting valencequarks.Comment: 11 pages, 2 figures, 6 tables; replaced with revised versio

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