X_0(2900) and X_1(2900): Hadronic Molecules or Compact Tetraquarks

Very recently the LHCb collaboration reported their observation of the first two fully open-flavor tetraquark states, the X_0(2900) of J^P = 0^+ and the X_1(2900) of J^P = 1^-. We study their possible interpretations using the method of QCD sum rules, paying special attention to an interesting feature of this experiment that the higher resonance X_1(2900) has a width significantly larger than the lower one X_0(2900). Our results suggest that the X_0(2900) can be interpreted as the s-wave D^*-K^*+ molecule state of J^P = 0^+, and the X_1(2900) can be interpreted as the p-wave \bar c \bar s u d compact tetraquark state of J^P = 1^-. Mass predictions of their bottom partners are also given.