Properties of N(1535) at finite density in the extended parity-doublet models

Abstract

We improve so called "naive" and "mirror" models for the positive and negative parity nucleons, N and N * , by introducing nonlinear terms allowed by chiral symmetry. Both models in this improvement reproduce the observed nucleon axial charge in free space and reveal interesting density dependence of the axial charges for N and N * , and the doublet masses. A remarkable difference between the two models is found in the off-diagonal axial charge, g AN N * , which could appear either as suppression or as enhancement of N * → πN decay in the medium.

Level crossing of particle–hole and mesonic modes in eta-mesonic nuclei

“…This picture has several interesting phenomenological consequences [34,35,38]. The important implication for the etameson physics is that the N * − N mass gap decreases in nuclear medium and at some density goes below the η mass [36,39]. This changes the sign of the η meson optical potential making it repulsive at saturation density as found in [10][11][12].…”

“…An extended version of the naive model was proposed in Ref. [39] to implement the πNN * coupling in the model by introducing contact terms with two mesons. In the mirror model, N and N * form a chiral doublet.…”

Formation of mesic nuclei by reactions

“…In the chiral doublet model together with the assumption of partial restoration of chiral symmetry, a reduction of the mass difference of N and N * in the medium is found to be in the mean field approximation as [36,37,43,44],…”

Mesons in Nuclei and Partial Restoration of Chiral Symmetry

“…The reduction is estimated as about 150 MeV at the saturation density in a chiral doublet model [37]. This implies that the energy of the N * -h mode gets lower in nuclear matter and at a certain density the level crossing of the η and N * -h modes takes place [39] as shown as the thin solid and dashed lines in Fig.…”