Tetraquark state candidates: Y(4260), Y(4360), Y(4660), and Z_c(4020/4025)

In this article, we construct the axialvector-diquark-axialvector-antidiquark type tensor current to interpolate both the vector- and the axialvector-tetraquark states, then calculate the contributions of the vacuum condensates up to dimension 10 in the operator product expansion, and we obtain the QCD sum rules for both the vector- and the axialvector-tetraquark states. The numerical results support assigning the Z_c(4020/4025) to be the J^PC = 1^+- diquark-antidiquark type tetraquark state, and assigning the Y(4660) to be the J^PC = 1^-- diquark-antidiquark type tetraquark state. Furthermore, we take the Y(4260) and Y(4360) as the mixed charmonium-tetraquark states, and we construct the two-quark-tetraquark type tensor currents to study the masses and pole residues. The numerical results support assigning the Y(4260) and Y(4360) to be the mixed charmonium-tetraquark states. (orig.)