Isospin as a spontaneously broken symmetry of the electroweak interactions

We consider an electroweak model based on the gauge group SU(2${)}_L$×U(1${)}_Y$×U(1${)}_X$×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${)}_L$×SU(2${)}_R$ 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¯ 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.