ORIGIN OF AND BOUND ON THE NON-HERMITICITY OF EFFECTIVE INTERACTIONS

We show that the degree of non-Hermiticity of the standard effective i nteraction, R, is determined by the eigenvalues, mu2, of the operator omega(dagger)omega, where omega is the operator which maps the model s pace states onto the excluded space. Both a formal bound and a model c alculation show that if the values of mu2 are small or state independe nt, the non-Hermiticity is small. Similar considerations govern the ac curacy of approximating the exact Hermitian effective interaction, W, by 1/2 (R + R(dagger)).