Towards the quark mass dependence of $T_{cc}^{+}$ from lattice QCD

The $D{D}^{\ast }$ scattering phase shifts in the $T_{cc}^{+}=cc\bar{u}\bar{d}$ channel are extracted from lattice QCD for five different charm quark masses and a fixed light-quark mass corresponding to $m_{\pi }\simeq 280$~MeV. The phase shifts are analysed employing two approaches: effective range expansion and Lippmann–Schwinger equation derived in the effective field theory. In the latter case, the results imply an attraction at short range parametrised by contact terms and a slight repulsion at long range mediated by one-pion exchange with $m_{\pi }>m_{D^{\ast }}-m_D$. The poles in the amplitude across the complex energy plane are extracted and their trajectories are discussed as the charm quark mass is varied. Two complex conjugate poles corresponding to a resonance below threshold are found for $m_c$ close to the physical value. They turn into a pair of virtual states at the largest $m_c$ studied. With further increasing $m_c$, one virtual pole representing $T_{cc}^{+}$ is expected to move towards the two-body threshold and turn into a bound state. The light-quark mass dependence of the $T_{cc}^{+}$ pole is briefly discussed using the data on $D{D}^{\ast }$ scattering from other lattice collaborations.