The chiral partner of the nucleon in the mirror assignment with global symmetry

We calculate the pion-nucleon scattering lengths $a_0^{(\pm )}$ and the mass parameter $m_0$, which describes the nucleon mass in the chiral limit, at tree-level in the framework of a globally symmetric linear sigma model with parity-doubled nucleons. When recent lattice results [Takahashi] are used, we obtain $m_0\simeq 300-600$ MeV. While $a_0^{(-)}$ is in fair agreement with experimental data, $a_0^{(+)}$ is too small because of the employed large scalar meson mass. This indicates the need to account for additional scalar degrees of freedom.