Dirac gaugino from grand gauge-Higgs unification

Abstract

Abstract We show that models of the Dirac gaugino can naturally be embedded into a kind of grand unified theory (GUT), the grand gauge-Higgs unification (gGHU) model, with the gauge group $SU(5)\times SU(5)/\mathbb {Z}_2$ on an $S^1/\mathbb {Z}_2$ orbifold. The supersymmetric gGHU is known to possess a light chiral adjoint supermultiplet after the GUT breaking, thanks to the exchange symmetry of two SU(5) groups. Identifying the “predicted” adjoint fermion with the Dirac partner of the gaugino, we argue that the supersoft term, responsible for the Dirac gaugino mass, can be obtained from the supersymmetric Chern–Simons (CS)-like term in the gGHU setup. Although the latter term does not respect the exchange symmetry, we propose a novel way to introduce its breaking effect within a consistent orbifold construction. We also give a concrete setup of fermion field contents (bulk and boundary-localized fermions) that induce the requisite CS-like term, and calculate its coefficient from the bulk profile of chiral fermion zero modes. Our gGHU setup may be regarded as an extra-dimensional realization of the Goldstone gaugino scenario that was proposed before as a solution to the problem of adjoint scalar masses.