Spectrum of $[cq][\bar{s}\bar{q}]$ tetraquarks: Nature of $D_{s0}^{\ast }(2317)$, $D_{s1}(2460)$ and $T_{c\bar{s}0}^{\ast }(2900)$

Motivated by the recent observations of exotic open-charm tetraquark candidates $T_{c\bar{s}0}^a(2900{)}^{++}$ and $T_{c\bar{s}0}^a(2900{)}^0$, we systematically calculate the mass spectra of $[cq][\bar{s}\bar{q}]$ tetraquarks within a nonrelativistic constituent quark potential model. In the model, the tetraquark states are treated as diquark-antidiquark bound systems with an interior interaction similar to the quark-antiquark interaction in conventional mesons. The well established states $D_{s0}^{\ast }(2317)$ with $J^P=0^{+}$ and $D_{s1}(2460)$ with $J^P=1^{+}$ could be identified as the two ground states of the $[cq][\bar{s}\bar{q}]$ system. $T_{c\bar{s}0}^a(2900{)}^0$ and $T_{c\bar{s}0}^a(2900{)}^{++}$ could be naturally interpreted as radially excited $0^{+}$ tetraquark states with different interior components. Their large mass difference may result from their different interior structure instead of an isospin symmetry breaking. Whether $T_{c\bar{s}0}^a(2900{)}^0$ and $T_{c\bar{s}0}^a(2900{)}^{++}$ belong to an isospin triplet deserves further experimental investigation. In addition, there may be another $0^{+}$ $[cq][\bar{s}\bar{q}]$ tetraquark state with mass around $2450$ MeV, which is composed of a $cq$ diquark and a $\bar{s}\bar{q}$ antidiquark both with spin-0. In the energy region $2640-2700$ MeV, there may be a $J^P=2^{+}$ $[cq][\bar{s}\bar{q}]$ tetraquark state composed of the $cq$ diquark and the $\bar{s}\bar{q}$ antidiquark both with spin-1.