Elusive exotic states

The existence of flavor exotic QQqq molecular-type states is investigated. An attractive force between two pseudoscalar H = (Qq) 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∗ Hπ vertex. For a g value calculated from the experimental upper limit on the width of the D∗ 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 ≈ 2 mH and flavor quantum number ±2.