Chiral partner structure of light nucleons in an extended parity doublet model

Abstract

We study chiral partner structure of four light nucleons, N (939), N (1440), N (1535) and N (1650) using an effective chiral model based on the parity doublet structure. In our model we introduce four chiral representations, (1, 2), (2, 1), (2, 3) and (3, 2) under SU(2)L ⊗ SU(2)R symmetry. We determine the model parameters by fitting them to available experimental values of masses, widths and the axial charge of N (939) together with the axial charges of N (1535) and N (1650) by lattice analyses. We find five groups of solutions: In a group the chiral partner to N (939) is N (1440) having small chiral invariant mass. In another group, the chiral partner is a mixture of N (1535) and N (1650) having a large chiral invariant mass. We claim that off-diagonal elements of axial-charge matrix can be used for distinguishing these groups. We also discuss changes of masses associated with chiral symmetry restoration, which could emerge in high density matter.

Constraint to chiral invariant masses of nucleons from GW170817 in an extended parity doublet model

“…In this section, we introduce an extended parity doublet model to describe nuclear matter based on the model constructed in Ref. [17]. The model includes four baryon fields corresponding to the following representations under SU(2) L ×SU(2) R chiral symmetry:…”

“…The parity doublet structure is extended to include hyperons and/or more nucleons in e.g., Refs. [5][6][7][8][9][10][11][12][13][14][15][16][17]. In Ref.…”

“…In Ref. [17], the authors of present paper constructed a model which includes two chiral representations, the [(2, 3) ⊕ (3, 2)] representation under SU(2) L ⊗ SU(2) R in addition to [(1, 2) ⊕ (2, 1)] representation, to study four nucleons, N (939), N (1440), N (1535) and N (1650). It was shown that there are wide range of two chiral invariant masses satisfying vacuum properties of the nucleons; the masses, the axial charges and the pionic decay widths, and that the solutions are categorized into five groups.…”

“…In this paper, we construct nuclear matter and neutron star matter using the model introduced in Ref. [17] based on the mean field approximation. For the meson parts, we use the model introduced in Ref.…”

“…This paper is organized as follows: In section II, we include the ω and ρ mesons into the model introduced in Ref. [17]. We give formulations to study nuclear matter in the mean field approximation in section III.…”