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Chiral unitary approach to hadron spectroscopy

E. Oset·T. Inoue·M. J. Vicente Vacas·A. Ramos·C. Bennhold
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Abstract

The s-wave meson-baryon interaction in the $S = -1$, $S= 0$ and $S= -2$ sectors is studied by means of coupled channels, using the lowest-order chiral Lagrangian and the N/D method or equivalently the Bethe-Salpeter equation to implement unitarity. This chiral approach leads to the dynamical generation of the $Λ(1405)$, $Λ(1670)$ and $Σ(1620)$ states for $S = -1$, the $N^*(1535)$ for $S= 0$ and the $Ξ(1620)$ for $S= -2$. We look for poles in the complex plane and extract the couplings of the resonances to the different final states. This allows identifying the $Λ(1405)$ and the $Λ(1670)$ resonances with $\bar{K}N$ and $KΞ$ quasibound states, respectively. Our results are found to be incompatible with the measured properties of the $Ξ(1690)$ resonance, thus ruling this state out as the remaining member of this octet of dynamically generated resonances. We therefore assign $1/2^-$ for the spin and parity of the $Ξ(1620)$ resonance as the $S=-2$ member of the lowest-lying $1/2^-$ octet.

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E. Oset, T. Inoue, M. J. Vicente Vacas, A. Ramos, C. Bennhold. 2002-09-05. Chiral unitary approach to hadron spectroscopy. https://doi.org/10.1142/s0217751x03014307

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