LEPTOPHOBIC Z' FROM SUPERSTRING DERIVED MODELS

It was recently suggested that the reported anomalies in R(b) and R(c) can be interpreted as the effect of a heavy vector boson that couples to quarks and is universally decoupled from leptons. We examine how a n extra gauge boson with this property can arise from superstring deri ved models. In a specific three generation model we show that the U(1) (B-L) symmetry combines with the horizontal flavor symmetries to form a universal leptophobic U(1) symmetry. In our model there is an enhanc ement of the color gauge group from twisted sectors. The enhancement o ccurs after the breaking of the unifying gauge symmetry by ''Wilson li nes''. The leptophobic U(1) symmetry then becomes a generator of the c olor SU(4) gauge group. We examine how similar symmetries may appear i n other string models without the enhancement, We propose that if the current LEP anomalies persist it may be evidence for a certain class o f un-unified superstring models.