If the gluon field tensor is represented as G μν, then the gluon condensate is the vacuum expectation value ⟨ ⟨ G μ μ ν ν G μ μ ν ν ⟩ ⟩ . It is not clear yet whether this condensate is related to any of the known phase changes in quark matter. There have been scattered studies of other types of gluon condensates, involving a different number of gluon fields.