Minimal Supersymmetric $SU(4)\times SU(2{)}_L\times SU(2{)}_R$

We present a minimal string-inspired supersymmetric $SU(4) \times SU(2)_L \times SU(2)_R$ model, and provide a detailed analysis of the symmetry breaking potential in this model, based on a generalisation of that recently proposed by Dvali, Lazarides and Shafi. The model contains a global U(1) R-symmetry and reduces to the MSSM at low energies. However it improves on the MSSM since it explains the magnitude of its $\mu$ term and gives a prediction for $\tan \beta \simeq m_t/m_b$. It also predicts an essentially stable proton, and contains both cold' and hot’ dark matter candidates. A period of hybrid inflation above the symmetry breaking scale is also possible in this model. Finally it suggests the existence of `heavy’ charge $\pm e\mathrm{/}6$ (colored) and $\pm e\mathrm{/}2$ (color singlet) states.