X(3872) as a D-D* molecule bound by quark exchange forces
  The Bethe-Salpeter equation for the T-Matrix of D-D* scattering is solved with a meson-meson potential that results from 2nd order Born approximation of quark exchange processes. This potential turns out to be complex and energy dependent due to the pole contribution from the coupling to the intermediate J/psi-rho meson pair propagator. As a consequence, a bound state with a mass close to 3.872 GeV occurs in the J/psi-rho continuum. This result suggests that quark exchange forces may provide the solution to the puzzling question for the origin of the interaction which leads to a binding of D and D* mesons in the X(3872) state. 
Carlos Pena and David Blaschke
hep-ph nucl-th