  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. The obtained structure of one-meson exchange interaction confirms a
prediction of the large $N_c$ limit approach stating that the mass splitting
between various baryon states receive 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 $\Delta^*(3/2^-)$ 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.

High Energy Physics - Phenomenology;Nuclear Theory