Experimental limit on the decay τ-→ντK-K0

We set an upper limit on the branching fraction B(τ-→ντK-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-→ντK-K0 is related via SU(3) to the second-class-current decay τ-→ντπ-η. Our limit is nearly 20 times smaller than the recently reported branching fraction B(τ-→ντπ-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-→ντK*-)=(1.5±0.4*0.4%.