Chiral doublet model for the positive and negative parity nucleons
We discuss the properties of the nucleon (N) and its excited state with odd parity (N*) under the aspect of chiral symmetry, identifying them with suitable representations of the chiral group. It is shown that there are two distinctive schemes to assign the chiral multiplet to N and N*. We construct linear sigma models for N and N* with the two assignments to show their physical implications. We also discuss the in-medium properties of N(1535), comparing the present model with the other chiral model based on the different picture of N*.