How to understand the $X(2900)$?

In this work, the $S$- and $P$-wave ${\bar{D}}^{\ast }{K}^{\ast }$ interactions are studied in a coupled-channel formalism to understand the recently observed $X_0(2900)$ and $X_1(2900)$ at LHCb. The experimental event distributions can be well described, and two states with $I(J^P)=0(0^{+})$ and $0(1^{-})$ are yielded in an unified framework. The masses of the $0^{+}$ and $1^{-}$ states are consistent with the experimental data, but the width of the $0^{+}$ state is larger than that of the $1^{-}$ one. The $X_1(2900)$ can be interpreted as the $P$-wave excitation of the ground-state $X_0(2900)$ in the hadronic molecular picture. The $S$- and $P$-wave multiplets in the ${\bar{D}}^{\ast }{K}^{\ast }$ system have many members, so the present peak in the $D^{-}{K}^{+}$ invariant mass distributions might contain multi subpeaks. In order to probe the fine structures behind the single whole peak now, more refined measurements in the $B^{+}\to D^{+}{D}^{-}{K}^{+}$ decay channel are necessary.