“…[20], Guo, Meissner and Zou provide additional arguments using the chiral symmetry and heavy quark symmetry. According to the constituent quark model, the constituent diquark model, the chiral symmetry and heavy quark symmetry, the lowest mass of the subd tetraquark state with J P = 0 + is much larger than the M X(5568) [19,20,21], for more references on this subject, one can consult Refs. [19,20].…”