Coupling constant and quark-loop expansion for corrections to the valence approximation

For full QCD vacuum expectation values we construct an expansion in quark-loop count and in powers of a coupling constant. The leading term in this expansion is the valence (quenched) approximation vacuum expectation value. Higher terms give corrections to the valence approximation. A test of the expansion is presented for moderately heavy quarks on a small lattice. We consider briefly an application of the expansion to quarkonium-glueball mixing. © 1999 The American Physical Society.