Mass spectra and electromagnetic characteristics of the $K^{(*)}\bar D^{(*)}$ and $K^{(*)}{D}^{(*)}$ molecular tetraquarks from the coupled-channel dynamics

Abstract

Motivated by the observation of numerous charmed-strange hadrons lying close to the $K^{(*)}\bar D^{(*)}$ and $K^{(*)}D^{(*)}$ thresholds, we systematically investigate their mass spectra and electromagnetic characteristics, explicitly incorporating the $S$-$D$ wave mixing and coupled-channel effects. For the mass spectra, we employ the one-boson-exchange model and obtain several promising $K^{(*)}\bar D^{(*)}$ and $K^{(*)}D^{(*)}$ molecular candidates awaiting future experimental confirmation. The coupled-channel dynamics is found to play an essential role: it not only enhances binding in existing channels but also generates new loosely bound states that are absent in the single-channel approximation. Regarding the electromagnetic characteristics, we discuss the M1 radiative decay widths and magnetic moments of these charmed-strange molecular tetraquarks based on our obtained mass spectra and spatial wave functions within the constituent quark model. Our results demonstrate that the electromagnetic observables serve as valuable discriminants for clarifying the nature of these hadronic molecules. We encourage experimental collaborations to focus on such predicted charmed-strange molecular tetraquark candidates, especially the genuinely exotic $K^{(*)}\bar D^{(*)}$ states comprising four different flavors with valence quark content $\bar c \bar s u d$.