The $J\mathrm{/}\psi D{D}^{\ast }$ vertex

We employ QCD sum rules to calculate the $J\mathrm{/}\psi D{D}^{\ast }$ form factors and coupling constant by studying the three-point $J\mathrm{/}\psi D^{\ast }D$ correlation function. We find that the momentum dependence of the form factor depends on the off-shell meson. We get a value for the coupling which is in agreement with estimates based on constituent quark model.