Phenomenological analysis of a topless left-right model

We reanalyze a topless left-right model due to Ma, after allowing flavor-changing neutral currents which are consistent with all the experimental limits coming from flavor-changing processes. The resulting model can naturally reproduce the observed values of $B_d^0-{\overline{B}}_d^0$ mixing, where the original model had failed by 8 orders of magnitude. Thus, the model is viable from the viewpoint of low-energy phenomenology. In the case of $Z^0$ physics, however, we see that the model makes distinctive predictions for some of the $Z^0\to f\overline{f}$ partial widths due to the nonstandard couplings of the fermion $f$. The recent measurements of these partial widths from CERN LEP seem to clearly rule out this model. Indeed the precision measurement of the $Z^0\to b\overline{b}$ partial width along with the known properties of $b$ decay seems to rule out any topless model.