The electroweak theory is the unified field theory of the electromagnetic and weak interactions. The gauge group is U(1) x SU(2). The gauge particles are the photon, and the Z, W+ and W- - particles. The W+ and W- - particles have the electric charges +- e , respectively, which means that the electroweak field couples to itself. So the field equations are nonlinear, unlike in the electromagnetic theory, which is linear.