# Dirac shell quark-core model for the study of non-strange baryonic spectroscopy

## TL;DR

This paper introduces a Dirac shell model for baryon spectroscopy that incorporates a scalar particle to ensure translational invariance, reproducing spectra similar to quark-diquark models and matching experimental data.

## Contribution

The paper develops a Dirac shell model with a scalar particle to study baryon spectra, avoiding translational invariance issues and considering one-particle excitations with a two-quark core.

## Key findings

- Successfully reproduces N and Δ resonance spectra
- Calculates nucleon magnetic moments consistent with experiments
- Provides a framework comparable to quark-diquark models

## Abstract

A Dirac shell model is developed for the study of baryon spectroscopy, taking into account the most relevant results of the quark-diquark models. The lack of translational invariance of the shell model is avoided, in the present work, by introducing a scalar-isoscalar fictitious particle that represents the origin of quark shell interaction; in this way the states of the system are eigenstates of the total momentum of the baryon. Only one-particle excitations are considered. A two-quark core takes the place of the diquark, while the third quark is excited to reproduce the baryonic resonances. For the $N(939)$ and $\Delta(1232)$, that represent the ground states of the spectra, the three quarks are considered identical particles and the wave functions are completely antisymmetric. The model is used to calculate the spectra of the $N$ and $\Delta$ resonances and the nucleon magnetic moments. The results are compared to the present experimental data. Due to the presence of the core and to the one-particle excitations, the structure of the obtained spectra is analogous to that given by the quark-diquark models.