Narrow Results

The dependence of the nucleon mass on the pion mass is studied in the framework of the extended quark sigma model. We apply the modified quark sigma model to analyze the pion–nucleon sigma term. Analytic expressions are derived using the Feynman–Hellman theorem. The field equations are solved in the mean-field approximation. The results are compared with the CP-PACS group and the cloudy bag model. The results indicate that the extended linear sigma model provides good agreement compared to other models in the mean-field approximation.

We review recent progress in our understanding of the role of strange quarks in the structure of the nucleon. For the contribution to its mass the result is remarkably small, an order of magnitude smaller than commonly assumed. This has profound consequences for the searches for dark matter which are currently underway. There has also been remarkable progress in the understanding of hypernuclei. In particular, there is a very natural explanation at the quark level of why Λ-hypernuclei are bound whereas Σ-hypernuclei are not. The consequences for dense matter, for example in neutron stars, are not yet fully understood but we know they are significant.

We review recent progress in our understanding of the role of strange quarks in the structure of the nucleon. For the contribution to its mass the result is remarkably small, an order of magnitude smaller than commonly assumed. This has profound consequences for the searches for dark matter which are currently underway. There has also been remarkable progress in the understanding of hypernuclei. In particular, there is a very natural explanation at the quark level of why Λ-hypernuclei are bound whereas Σ-hypernuclei are not. The consequences for dense matter, for example in neutron stars, are not yet fully understood but we know they are significant.