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 $m_{ 0}\simeq300-600$ 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.
Categories: hep-ph