In the framework of the one-boson-exchange model, we explore whether the intermediate- and short-range forces from $\sigma /\omega$ exchange can be strong enough to bind heavy molecular states. ${\mathrm{\Lambda }}_{c}D(\overline{D})$ and ${\mathrm{\Lambda }}_c{\mathrm{\Lambda }}_c({\overline{\mathrm{\Lambda }}}_c)$ systems have been studied and compared. We find that the force from $\sigma$ exchange is attractive and dominant, whereas the $\omega$-exchange force is not. As a consequence, the S-wave ${\mathrm{\Lambda }}_{c}D$, ${\mathrm{\Lambda }}_c{\mathrm{\Lambda }}_c$, and ${\mathrm{\Lambda }}_c{\overline{\mathrm{\Lambda }}}_c$ can be possible molecular candidates. We further indicate that a one hadron-hadron system with more light quarks $(u,d)$ can be easier to form than a bound state. As a by-product, by studying the heavy-quark mass dependence for the ${\mathrm{\Lambda }}_{c}D(\overline{D})$-like and ${\mathrm{\Lambda }}_c{\mathrm{\Lambda }}_c({\overline{\mathrm{\Lambda }}}_c)$-like systems, we find that the charm/bottom sector can easily accommodate molecular states. Finally, the ${\mathrm{\Lambda }}_{c}N(\overline{N})$ and ${\mathrm{\Lambda }}_{b}N(\overline{N})$ systems are investigated. Our results indicate that they are also likely to form bound states. By including one-$\pi$-exchange forces, providing additional attraction when coupled channels are included, we expect many molecular states in heavy-quark sectors.

• Received 29 July 2017

DOI:https://doi.org/10.1103/PhysRevD.96.116012