Predicting charmed-strange molecular tetraquarks with $K^{(\ast )}$ and $T$-doublet (anti-)charmed meson

In this work, we systematically investigate the charmed-strange molecular tetraquarks composed of a $K^{(\ast )}$ meson and a $T$-doublet (anti-)charmed meson. Our analysis is performed within the one-boson-exchange model, with a careful treatment of $S$-$D$ wave mixing and coupled-channel effects. We identify the $X_1(2900)$ resonance, observed by LHCb, as a molecular state in the coupled $K{\bar{D}}_1\mathrm{/}{K}^{\ast }{\bar{D}}_1\mathrm{/}{K}^{\ast }{\bar{D}}_2^{\ast }$ system with quantum numbers $I(J^P)=0(1^{-})$. This state is dominated by the $K{\bar{D}}_1$ component but exhibits a significant admixture from the $K^{\ast }{\bar{D}}_1$ channel. Furthermore, we predict several partner states of the $X_1(2900)$ in the $K^{\ast }{\bar{D}}_1$ and $K^{(\ast )}{\bar{D}}_2^{\ast }$ systems. We also extend our framework to the $K^{(\ast )}{D}_1\mathrm{/}{K}^{(\ast )}{D}_2^{\ast }$ systems, where our results suggest a series of $T_{c\bar{s}}$-type charmed-strange molecular tetraquark candidates. These findings provide a comprehensive picture of the molecular spectrum in the charmed-strange sector and can be tested in future experimental studies.