Isospin as a spontaneously broken symmetry of the electroweak interactions

We consider an electroweak model based on the gauge group SU(2)/sub L/ x U(1)/sub Y/ x U(1)/sub X/ x D with isospin as a spontaneously broken symmetry, and D a discrete symmetry which interchanges the two U(1)'s. The new physics is characterized by the vacuum expectation value of a Higgs triplet with Majorana couplings to the leptons, and an extra heavier neutral vector boson. The model is compatible with a global SU(2)/sub L/ x SU(2)/sub R/ symmetry which is extended to the Yukawa and Majorana sectors of the theory. The model also suggests the existence of a triplet of colored scalar particles with Majorana couplings to the quarks, which generate the u-d quark mass difference by radiative corrections in a strong-coupling regime. Such colored scalar particles would be observed in the pp-bar collisions as dijets with large transverse missing energy, and the color singlets as like-sign isolated dimuon events. A dijet can simulate a monojet if one of the jets is hidden in the hadronic background