Dynamic critical behavior of a Swendsen-Wang-type algorithm for the Ashkin-Teller model

We study the dynamic critical behavior of a Swendsen-Wang-type algorithm for the Ashkin-Teller model. We find that the Li-Sokal bound on the autocorrelation time (tau(int), g greater than or equal to constxC(H)) holds along the self-dual curve of the symmetric Ashkin-Teller model, and is almost, but not quite sharp. The ratio tau(int)epsilon/C-H appears to tend to infinity either as a logarithm or as a small power (0.05 less than or similar to P less than or similar to 0.12). In an appendix we discuss the problem of extracting estimates of the exponential autocorrelation time.