Critical basis dependence in bounding R-parity breaking couplings from neutral meson mixing

Assuming one nonzero product of two lambda'-type couplings and working in t wo different bases for the left-handed quark superfields, the neutral meson mixings are used to bound these products. We emphasize the strong basis de pendence of the bounds: in one basis many products contribute to neutral me son mixings at tree level, while in the other these products except one con tribute at 1-loop level only and the GIM mechanism takes place. Correspondi ngly, these bounds differ between bases by orders of magnitudes. (C) 1999 E lsevier Science B.V. All rights reserved.