Exotic resonances due to η exchange

The meson X(3872) and several related states appear to be in large part hadronic molecules in which a heavy flavored meson (e.g., D-0) is bound to another heavy meson (e.g., (D) over bar*(0)). Although not the only contribution to the binding, pion exchange seems to play a crucial role in generating the longest-range force between constituents. Mesons without u and d light quarks (such as D-s) cannot exchange pions, but under suitable conditions can bind as a result of eta exchange. Channels in which this mechanism is possible are identified, and suggestions are made for searches for the corresponding molecular states, including a manifestly exotic baryonic Lambda(c)(D) over bar (s)* resonance decaying into J/psi Lambda. (C) 2016 Elsevier B.V. All rights reserved.