  The formulation of a grand unified field theory based on the nonlinearly
realized SU(5) gauge group is presented. The tree-level action is constructed
by requiring invariance under local left SU(5) gauge transformations, the
existence of a weak power-counting bound and by imposing also an additional
invariance under local right SU_C(3) X U_Q(1) transformations. The local
functional equation associated to this latter invariance allows one to prove
the absence of physical scalar modes with the quantum numbers of massless gauge
bosons from the perturbative spectrum. Two independent mass invariants for the
electroweak gauge bosons exist, although the gauge group of our model is
simple. The flavour sector of the model is analyzed and compared with the one
of the minimal Georgi-Glashow grand unified theory.
