  The vector representation of the linearized gravitational field (the graviton
field) or the so called quantum gravitodynamics which describes the motion of
masses in a weak gravitational field is employed to understand the unity of the
four known interactions. We propose a gauge group SU(3)xSU(2)xU(1)xU(1) for
such a unified field theory. In this paper we study the SU(2)xU(1)xU(1) sector
of the theory and in analogy to the electroweak mixing angle we define a
gravitoweak mixing angle. The unified gauge field theory predicts the existence
of three massive vector bosons, the Y+/- and the X^0. and two massless vector
bosons, the photon and the graviton (in its vector representation). We
determine the mass spectrum of the Y+/- and the X^0 and predict a modification
to the fine structure constant under unified field conditions. Furthermore, we
briefly discuss the implications of the extended object formulation for the
gauge hierarchy problem.
