2023 Impact factor 4.2
Particles and Fields
Eur. Phys. J. C 4, 115-127
DOI 10.1007/s100529800762

A chiral bag model with a soft surface : structure and solutions of the Fuzzy and the modified Fuzzy Bag Model

C.A.Z. Vasconcellos1 - H.T. Coelho2 - F.G. Pilotto3 - B.E.J. Bodmann1 - M. Dillig3 - M. Razeira1

1 Instituto de Física, Universidade Federal do Rio Grande do Sul CEP 91509-900 Porto Alegre, Brasil
2 Departamento de Física, Universidade Federal de Pernambuco CEP 50670-901 Recife, Brasil
3 Institut für Theoretische Physik III, Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany

Received: 10 March 1997 / Revised version: 14 October 1997 / Published online: 20 February 1998

Abstract
In the present work we propose a new bag model for hadrons, called the modified fuzzy bag model (MFBM). The distinguishing feature of this model is the suppression of the pion field, as it enters the bag, by means of a scalar potential for the pions, while still preserving chiral symmetry. The mechanism of pion suppression in the MFBM is similar to the mechanism of quark suppression in the fuzzy bag model (FBM). The standard chiral transformation for the pion field suffers a natural alteration in the MFBM, and as a result the model is chiral invariant. We present also a discussion of the FBM and study, in the quark sector, the implications of the soft surface of the bag on the expectation value of the mass operator. In the pion-quark sector, we study the effects of the suppression of the pion field on the form factor for the pion-nucleon interaction, on the pion-nucleon coupling constant $g_{ \pi {\scriptscriptstyle{N}} {\scriptscriptstyle{N}} }$and on the nucleon axial charge gA. Calculations of the pion-nucleon form factor exhibit, in particular, an improvement over previous results. The pionic axial current induces, in the MFBM, a nonvanishing and orientation dependent contribution to axial charge. An analysis of the asymptotic behaviour of the axial charge shows that the role of the surface is to increase the difference of the contributions associated to different orientations.


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