Higgs as (Pseudo-) Goldstone Particles Revisited

Abstract

Phenomenological consequences of a minimal supersymmetric model coupled to the N=l super­ gravity, in which Higgs fields are assigned to (pseudo·) Nambu-Goldstone particles associated with a suitable global symmetry, are compared with recent experimental constraints. In the simplest case of the hidden sector, the model encounters a serious difficulty of the existence of a light Higgs boson below about 20 GeV. However it is found that the model is still viable to describe experimental observations in a more general and interesting case where the hidden sector consists of Yang·Mills and chiral multiplets. The standard model of strong and electro weak interactions has been remarkably successful to describe experimental data. Recent experiments with new facilities showed no evidence for any deviation away from the standard model.!) However many people believe that the standard model should be extended to reduce its many arbitrary parameters, or to solve its principal difficulty of naturalness problem. Among various extensions, supersymmetry is very attractive because it can partially solve the naturalness problem of the gauge hierarchy by a beautiful symmetry principle. 2 ) It is also noticeable that almost all consistent string theories predict models with supersymmetry. The most troublesome problem in the standard model is concerned with the Higgs sector. Even in the supersymmetric model the Higgs sector is quite ambiguous, though the problem of quadratic divergences is absent due to the supersymmetry. Several years ago Takano and the present authors studied a minimal supersymmetric model coupled to the N = 1 supergravity, in which Higgs fields were assumed to be (pseudo-) Nambu-Goldstone particles associated with a suitable global symmetry.3) The global symmetry was assumed not to be disturbed by gravitational interactions. A remarkable feature of the scheme was that the mass terms of Higgs fields were strongly constrained by the symmetry principle. We gave in Ref. 3) numerical analyses by assuming that the top quark mass mt ~40 GeV, which was the expected value in those days.4) It will now be appropriate to reinvestigate phenomenological consequences of our scheme, because bounds on masses of the top quark and unknown particles have been substantially improved. 1 ),5)-9) In the rest of