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We have studied, using double ratio of QCD (spectral) sum rules, the ratio between the masses of $T_{cc}$ and X(3872) assuming that they are respectively described by the $D-{D}^*$ and $D-bar{D}^*$ molecular currents. We found (within our approximation) that the masses of these two states are almost degenerate. Since the pion exchange interaction between these mesons is exactly the same, we conclude that if the observed X(3872) meson is a $Dbar{D}^*+c.c.$ molecule, then the $DD^*$ molecule should also exist with approximately the same mass. An extension of the analysis to the $b$-quark case leads to the same conclusion. We also study the SU(3) breakings for the $T^s_{QQ}/T_{QQ}$ mass ratios. Motivated by the recent Belle observation of two $Z_b$ states, we revise our determination of $X_b$ by combining results from exponential and FESR sum rules.
The mass and coupling of the doubly charmed $J^P=0^{-}$ diquark-antidiquark states $T_{cc;bar{s} bar{s}}^{++}$ and $T_{cc;bar{d} bar{s}}^{++}$ that bear two units of the electric charge are calculated by means of QCD two-point sum rule method. Comput
Constituent mass predictions for axial vector (i.e., $J^P=1^+$) $cc$ and $bb$ colour antitriplet diquarks are generated using QCD Laplace sum-rules. We calculate the diquark correlator within the operator product expansion to NLO, including terms pro
The mass and coupling of the scalar tetraquark $T_{bb;overline{u}overline{d }}^{-}$ (hereafter $T_{b:overline{d}}^{-} $) are calculated in the context of the QCD two-point sum rule method. In computations we take into account effects of various quark
The spectroscopic parameters and decay channels of the scalar tetraquark $ T_{bb;overline{u}overline{s}}^{-}$ (in what follows $T_{b:overline{s} }^{-} $) are investigated. The mass and coupling of the $T_{b:s}^{-}$ are calculated using the two-point
The isospin breaking effect plays an essential role in generating hadronic molecular states with a very tiny binding energy. Very recently, the LHCb Collaboration observed a very narrow doubly charmed tetraquark $T_{cc}^+$ in the $D^0D^0pi$ mass spec