Vacuum phenomenology of the chiral partner of the nucleon in a linear sigma model with vector mesons

We investigate a linear sigma model with global chiral U(2)(R) x U(2)(L) symmetry. The mesonic degrees of freedom are the standard scalar and pseudoscalar mesons and the vector and axial-vector mesons. The baryonic degrees of freedom are the nucleon, N, and its chiral partner, N*, which is usually identified with N(1535). The chiral partner is incorporated in the so-called mirror assignment, where the nucleon mass is not solely generated by the chiral condensate but also by a chirally invariant mass term, m(0). The presence of (axial-) vector fields modifies the expressions for the axial-coupling constants of the nucleon, g(A)(N), and its partner, g(A)(N)*. Using experimental data for the decays N* -> N pi and a(1) -> pi gamma, as well as lattice results for g(A)(N*) we infer that in our model m(0) similar to 500 MeV, i.e., an appreciable amount of the nucleon mass originates from sources other than the chiral condensate. We test our model by evaluating the decay N* -> N eta and the s-wave nucleon-pion scattering lengths a(0)((+/-)).