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HK: Fachverband Hadronen und Kerne

HK 56: Hadron Structure and Spectroscopy I

HK 56.7: Vortrag

Mittwoch, 18. März 2009, 18:15–18:30, H-ZO 20

The chiral partner of the nucleon in the mirror assignment with global symmetry — •Susanna Gallas^1,2, Francesco Giacosa¹, and Dirk Rischke^1,2 — ¹Institute for theoretical physics, Goethe University, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main, Germany — ²Frankfurt Institute for Advanced Studies, Goethe University, Ruth-Moufang-Str. 1, D-60438 Frankfurt am Main, Germany

We calculate the pion-nucleon scattering lengths a₀^{(± )} and the mass parameter m₀, which describes the nucleon mass in the chirally restored phase for parity-doubled nucleons. This is done at tree-level in the framework of a linear sigma model with global chiral symmetry. We obtain m₀=300-600 MeV when using the recent lattice results of T.Takahashi and T. Kunihiro. While a₀⁽⁻⁾ is in fair agreement with experimental data, a₀⁽⁺⁾ is too small because of the employed large mass of the sigma meson. This indicates the need of an additional scalar degree of freedom, such as a scalar tetraquark state with a mass of about 500 MeV. In this framework the very existence of a light tetraquark is responsible of the stability of nuclear matter.