Implication of a negative effective range on the $D{\bar{D}}^{\ast }$ interaction and the nature of $X(3872)$

A recent analysis of the LHCb data [Phys. Rev. D 105 (2022) L031503] obtained a sizable negative effective range for the $X(3872)$. This has attracted intensive discussions on whether $X(3872)$ can be deemed as a $D{\bar{D}}^{\ast }$ molecular state. This work explicitly demonstrates that the negative effective range of the $X(3872)$ does not contradict the molecular picture, adopting an effective field theory formulation of the $D{\bar{D}}^{\ast }$ interaction that can simultaneously reproduce the binding energy and effective range of the $X(3872)$. We elaborate on the implications of the large negative effective range of $X(3872)$ and the small binding energy on the underlying $D{\bar{D}}^{\ast }$ interaction. Such results are relevant for a better understanding of hadronic molecules and their binding mechanism.