Faddeev calculation of pentaquark $\Theta^+$ in the Nambu-Jona-Lasinio model-based diquark picture

TL;DR

This study uses a Faddeev calculation within the NJL model to investigate the pentaquark $ heta^+$, finding no bound state in the positive parity channel but a bound state with negative parity under certain conditions.

Contribution

It applies a Bethe-Salpeter-Faddeev approach with NJL model to analyze the pentaquark structure in a diquark picture, exploring interactions and bound state possibilities.

Findings

${ar s}D$ interaction is attractive in s-wave

$DD$ interaction is repulsive in p-wave

No bound positive parity pentaquark found, negative parity bound state possible with strong coupling

Abstract

A Bethe-Salpeter-Faddeev (BSF) calculation is performed for the pentaquark $\Theta^+$ in the diquark picture of Jaffe and Wilczek in which $\Theta^+$ is a diquark-diquark-${\bar s}$ three-body system. Nambu-Jona-Lasinio (NJL) model is used to calculate the lowest order diagrams in the two-body scatterings of ${\bar s}D$ and $D D$. With the use of coupling constants determined from the meson sector, we find that ${\bar s}D$ interaction is attractive in s-wave while $DD$ interaction is repulsive in p-wave. With only the lowest three-body channel considered, we do not find a bound $ \frac 12^+$ pentaquark state. Instead, a bound pentaquark $\Theta^+$ with $ \frac 12^-$ is obtained with a unphysically strong vector mesonic coupling constants.