Leptophobic U(1)'s and the Rb-Rc anomalies.
Phys Rev D Part Fields 54:7 (1996) 4635-4647
Realizing Higher-Level Gauge Symmetries in String Theory: New Embeddings for String GUTs
(1996)
KINETIC MIXING AND THE SUPERSYMMETRIC GAUGE HIERARCHY
Nucl.Phys.B 492 (1996) 104