Aspects of left-right symmetric models in superstring phenomenology

The general features of low-energy, rank-six left-right symmetric models as inspired by the superstring are examined. Particular attention is paied to the mass-mixing matrix of the exotic and down-type quarks. It is found that the class of models based on the group SU(3)C x SU(2)L x SU(2)N x U(1)L x U(1)R is plagued with the problem of unnatural fine tuning. Models based on the other left-right group, namely SU(3)C x SU(2)L x SU(2)R x U(1)L x U(1)R, work rather well from the points of view investigated. In this case a parameter fitting is presented which is compatible with the lowering of the group rank by two units via radiative breaking, without conflicting either with weak universality or with lepton conservation. The unification scale comes in the 1017 GeV mass range, the intermediate (right-handed) scale is quite low, not exceeding the 104 GeV range, and the Weinberg angle is correct. Good prospects are also obtained for proton decay and neutrino masses. (orig.)