Effects of instanton induced interactions on pentaquarks

Roles of instanton induced interactions (III) in the masses of pentaquark baryons, ${\Theta }^{+}$ ($J=1/2$ and $3/2$) and ${\Xi }^{--}$, and a dibaryon, $H$, are discussed using the MIT bag model. It is shown that the two-body terms in III give a strong attraction mainly due to the increase of the number of flavor antisymmetric quark pairs in multiquark systems. In contrast, the three-body $u$-$d$-$s$ interaction is repulsive. It is found that III lowers the mass of negative-parity ${\Theta }^{+}$ as much as 100 MeV from the mass predicted by the bag model without III. We also consider possible quark model configurations for positive-parity ${\Theta }^{+}$ under III.

Figure 1

The masses of negative-parity pentaquarks, ${\Theta }^{+},{\Xi }^{--},{\Theta }_{S=3/2}^{+}$, and the dibaryon $H$. The dashed lines are the values at $P_{III}=0$.

Figure 2

The bag radii for the pentaquarks.

Figure 3

The mass splittings of ${\Theta }_{S=3/2}^{+}-{\Theta }^{+}$ and ${\Xi }^{--}-{\Theta }^{+}$.