Exotic decay modes of the nucleon resonance $N^{\ast }(1535)$ and the ${\theta }^{+}$ problem

Abstract

Baryon resonance state with strangeness $S=+1$ observed in systems $p{K}^0$ and $n{K}^{+}$ is interpreted as a result of the decay $N^{\ast +}\to p\eta$ of the well-known resonance $N^{\ast }(1535)$ (with spin-parity $j^P={1/2}^{-}$ and mass $m\approx 1.54$ GeV) and the subsequent oscillation $\eta \rightleftarrows K^0$. It is argued that the latter is noticeably enhanced by the neighbourhood of the $\eta$ and $K^0$ levels and the gluon exchanges of the "penguin" form.

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