Elusive exotic states

Abstract

The existence of flavor exotic $QQ\bar{q}\bar{q}$ molecular-type states is investigated. An attractive force between two {\it pseudoscalar} $H=(Q\bar{q})$ heavy meson is generated by (correlated) two-pion exchange. The emergence of a (loosely) bound state depends crucially on the value of the coupling constant $g$ of the $H^{\ast }H\pi$ vertex. For a $g$ value calculated from the experimental upper limit on the width of the $D^{\ast }$ meson the considered mechanism alone is strong enough to generate a bound state in the $BB$ system while the $DD$ system is very close to become bound. Such states, if exist, are stable with respect to strong interactions. They may be observed as stable scalar particles with the mass $M\approx 2m_H$ and flavor quantum number $\pm 2$.

Comments: 10 pages including 4 figures. RevTex and epsfig.sty are used. Accepted for publication in Phys. Lett. B