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##### On the hadronic neutron-proton mass splitting in chiral soliton models of valence quarks

**Authors**: T. Neuber and M. Fiolhais

**Ref.**: Europhysics Letters **25**, 571-577 (1994)

**Abstract**: In the framework of chiral soliton models of valence quarks with and without confinement, namely the chiral chromodielectric model and the linear sigma-model, the hadronic mass difference between the neutron and the proton is considered as a consequence of an up- and down-quark mass difference. In those models we described the nucleon as a chiral soliton which we endow with good quantum numbers and zero linear momentum by carrying out exact angular-momentum, isospin and linear-momentum projections. For a choice m(d) - m(u) approximately 3.2 MeV the experimental value for the hadronic neutron-proton mass difference is obtained in both models. This result contrasts with the application of the collective quantization methods to the same models for which the hadronic splitting resulting from a quark isospin symmetry-breaking term turns out to be too small.