Θ⁺ baryon, N^*(1685) resonance, and πN sigma term reexamined within the framework of a chiral soliton model

We reexamine the properties of the baryon antidecuplet Θ⁺ and N^*, and the πN sigma term within the framework of a chiral soliton model, focusing on their dependence on the Θ⁺ mass. It turns out that the measured value of the N^* mass, M_N* = 1686 MeV, is consistent with that of the Θ⁺ mass M_Θ⁺ = 1524 MeV by the LEPS collaboration. The N^* → Nγ magnetic transition moments are almost independent of the Θ⁺ mass. The ratio of the radiative decay width Γ_nn* to Γ_pp* turns out to be around 5. The decay width for Θ⁺ → NK is studied in the context of the LEPS and DIANA experiments. When the LEPS value of the Θ⁺ mass is employed, we obtain Γ_ΘNK = (0.5 ± 0.1) MeV. The πN sigma term is found to be almost independent of the Θ⁺ mass. In addition, we derive a new expression for the πN sigma term in terms of the isospin mass splittings of the hyperon octet as well as that of the antidecuplet N^*. (author)