KK¯molecules

We have extended and improved our previous studies of the $\mathrm{qq}\overline{q}\overline{q}$ system, paying special attention to the $K\overline{K}$ channels. The new results clarify and reinforce the $K\overline{K}$ molecule interpretation of the $S^{*}$ and $\delta$. Effective meson-meson potentials extracted from the $\mathrm{qq}\overline{q}\overline{q}$ system and couplings to $q\overline{q}$ scalar mesons lead to coupled-channel amplitudes which closely resemble those observed in both the $S^{*}$ and $\delta$ channels. We also show that the $K\overline{K}$ molecules have properties consisent with experimental results on the production of the $S^{*}$ and $\delta$ and of low-mass $K\overline{K}$ pairs.