  We study the behavior of the isovector scalar correlator, which is
particularly sensitive to lattice artifacts, using domain-wall valence quarks
on a staggered sea (generated by the MILC collaboration). We analyze this
according to the prediction from chiral perturbation theory determined by
Prelovsek, which indicates that the leading unitarity violations come from
taste breaking effects. We show that our data behaves in the way predicted by
Prelovsek, thus verifying that the largest contribution to the violations of
unitarity which arise at finite lattice spacing can be described by the
mixed-action chiral perturbation theory.
