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An SU(4) × SU(2)L× SU(2)Rstring model with direct unification at the string scale

Physics Letters B
Publication Date
DOI: 10.1016/0370-2693(93)90132-2
  • Astronomy
  • Philosophy
  • Physics


Abstract We derive from a superstring a simple GUT with direct unification of gauge coupling constants at the string scale, i.e., M x ≈ 10 18GeV ≈ M string, irrespective of the string threshold effects, by fermionic construction. It is a D-parity violated supersymmetric SU(4) × SU(2) L × SU(2) R (Pati-Salam) model which breaks to the supersymmetric standard model at an intermediate sca M R and a massless spectrum which contains at M X the three generations of quarks and leptons, two Higgs multiplets in the representation ( 4, 1, 2) + ( 4 , 1, 2) plus one Higgs multiplet in ( 1, 2, 2). By identifying M X with the effective string unification scale M ̂ string  M string exp( π 6 ) in which a small string threshold correction has been taken into account, the mass scales can be selfconsistently fixed as M X ≈ 6.3 × 10 17 GeV, M R ≈ 6.4 × 10 11 GeV and M S (the supersymmetry breaking scale) ≈ 2.0 TeV in terms of the renormalization group equations. The scale M R might give new insight into phenomenology. For example, it produces a cosmologically interesting τ-neutrino mass in the 10 eV range owing to the see-saw mechanism with Majorana τ-neutrino mass ≈ 10 12 GeV.

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