CONSTRAINTS ON LIGHT TOP SQUARK FROM B-0-(B)OVER-BAR-(0) MIXING

We discuss the constraints on the mass of the lighter top squark from B-0-<(B)over bar(0)> mixing in the minimal supersymmetric standard mod el. A light top squark whose mass is less than half of the Z(0)-boson mass has not yet been excluded from direct search experiments at LEP. However, the existence of the light top squark may exceedingly enhance B-0-<(B)over bar(0)> mixing, owing to the box diagrams exchanging the charginos and the up-type squarks. We show that for a sizable region of parameter space the light top squark contribution to B-0-<(B)over b ar(0)> mixing becomes the same order of magnitude as the standard W-bo son contribution. Taking into account the experimental results for B-0 -<(B)over bar(0)> and K-0-<(K)over bar(0)> mixings, the existence of t he light top squark is excluded in an appreciable region of the parame ter space which LEP experiments have not ruled out.