Is X(3872) a molecule?
  We show that the literature on pion exchange between charm and bottom mesons is inconsistent. We derive the formalism explicitly, expose differences between papers in the literature and clarify the implications. We show that the X(3872) can be a bound state but that results are very sensitive to a poorly constrained parameter. We confirm that bound states in the B Bbar sector are possible. The circumstances whereby exotic combinations can bind with cc or bb quantum numbers are explored. 
C. E. Thomas, F. E. Close