Extended chiral transformations including diquark fields as parameters

We introduce an extended chiral transformation, which depends both on pseudoscalar and diquark fields as parameters, and determine its group structure. Assuming soft symmetry breaking in the diquark sector, the bosonisation of a quasi-Goldstone ud-diquark is performed. In the chiral limit the ud-diquark mass is defined by the gluon condensate, mud ≃300 MeV. The diquark charge radius is 12≃0.5 fm.