Experimental limit on the decay τ--->ντK-K0

We set an upper limit on the branching fraction B(τ^--->ν_τK^-K⁰)<0.26% at the 95% confidence level. The data sample was obtained with the TPC/Two-Gamma detector facility at the SLAC e⁺e^- storage ring PEP. The process τ^--->ν_τK^-K⁰ is related via SU(3) to the second-class-current decay τ^--->ν_τπ^-η. Our limit is nearly 20 times smaller than the recently reported branching fraction B(τ^--->ν_τπ^-η) of (5.1+/-1.0+/-1.2)%, whereas SU(3) symmetry predicts the ratio of πη to KK¯ production to be at most 5:1. We also measure the branching fraction B(τ^--->ν_τK^*-)=(1.5+/-0.4*0.4%.