  The principal purpose of meson spectroscopy is to understand the confining
force, which is generally assumed to be based on low-energy QCD. This is
usually done in the context of quark models that ignore the dynamical effects
of quark-pair creation and decay. Very recent lattice calculations confirm much
earlier model results showing that neglecting such effects, in the so-called
quenched approximation, may give rise to discrepancies of hundreds of MeV, and
so distort the meson spectra resulting from quark confinement only. Models
attempting to mimic unquenching through a redefinition of the constituent quark
mass or screening of the confining potential at larger interquark separations
are clearly incapable of accounting for the highly non-perturbative and
non-linear effects on mesonic bound-state and resonance poles, as demonstrated
with several published examples.
