The negative-energy dependence of the En-p mixing parameter and the pion cut

In order to study the effect of the pion cut on the 3S1 — 3D1n-p mixing parameter, we consider the negative-energy behaviour of the quantity τ = tan(2ε)/(2k2), where ε is the eigen-mixing parameter. The results are consistent with our earlier finding that the experimental data can be fitted without including effects due to the pion cut. However, τ is a sensitive function of energy near the pion-exchange branch point of the S matrix.