We present preliminary results for the chiral behavior of charged
pseudo-Goldstone-boson masses and decay constants. These are obtained in
simulations with N_f=2+1 flavors of tree-level, O(a)-improved Wilson sea
quarks. In these simulations, mesons are composed of either valence quarks
discretized in the same way as the sea quarks (unitary simulations) or of
overlap valence quarks (mixed-action simulations). We find that the chiral
behavior of the pseudoscalar meson masses in the mixed-action calculations
cannot be explained with continuum, partially-quenched chiral perturbation
theory. We show that the inclusion of O(a^2) unitarity violations in the chiral
expansion resolves this discrepancy and that the size of the unitarity
violations required are consistent with those which we observe in the
zero-momentum, scalar-isotriplet-meson propagator.Comment: 7 pages, 3 figures, talk by L. Lellouch at the XXV International
Symposium on Lattice Field Theory (LATTICE 2007), 30 July - 4 August 2007,
Regensburg, German
