  Most models for the strong decay of mesons, as well as unquenched quark
models which incorporate the effect of coupling to meson-meson channels, assume
that the coupling is driven by the creation of a quark-antiquark pair in spin
triplet. Their matrix elements can be factorised into a sum over
(model-dependent) spatial matrix elements multiplied by (model-independent)
coefficients. A general expression for these coefficients is obtained, and
their properties are studied. Numerical tables of the coefficients can be used
as a starting point for future calculations. The coefficients lead to
model-independent predictions for decay amplitudes and widths, and can explain
how mass shifts in the unquenched quark model do not spoil successful
predictions of the ordinary (quenched) quark model. This article is based on
work which will be presented in a forthcoming paper.
