Bochum 2009 – scientific programme
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HK: Fachverband Hadronen und Kerne
HK 56: Hadron Structure and Spectroscopy I
HK 56.7: Talk
Wednesday, March 18, 2009, 18:15–18:30, H-ZO 20
The chiral partner of the nucleon in the mirror assignment with global symmetry — •Susanna Gallas1,2, Francesco Giacosa1, and Dirk Rischke1,2 — 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.