Diquarks in tetraquark spectroscopy

The diquark is a system of two strongly correlated quarks. Obviously no free diquarks can exist, since they carry color. However they can theoretically form inside hadrons. While the actual possibility that two quarks can form stable bounds inside hadrons is still discussed, the use of a diquark effective degree of freedom can be very useful because it reduces the total number of states predicted and simplify the interactions inside hadrons. Here we present a possible application of the diquark to the tetraquark meson in the diquark-antidiquark limit. In this limit the tetraquark meson is composed of a diquark and an antidiquark. The complete set of states are constructed and a simple algebraic mass formula is applied in order to calculate the spectrum.