A SUPERSYMMETRIC SP(L)(6)XU(Y)(1) MODEL

A supersymmetric Sp(L) (6) x U-y(1) model (SUSY Sp(6)) is proposed as an extension of the standard electroweak model. The model is applied i n a phenomenological study of B-d(0)<(B)over bar (0)(d)> mixing. It is found that the supersymmetric (SUSY) partner (z) over tilde'$ of the extra Z' can significantly cancel the other contributions to bring the mixing parameter x(d) within the experimentally allowed range 0.57 le ss than or similar to 0.77 for a top mass of 158 less than or similar to m(t) less than or similar to 194 GeV. Other interesting and possibl y novel features of flavor-changing neutral currents (FCNC) in SUSY th eories with horizontal gauge symmetries are pointed out.