How sensitive are various NN observables to changes in the $\pi NN$ coupling constant?

Abstract

The deuteron, NN analyzing powers A_y, and the singlet scattering length show great sensitivity to the $\pi NN$ coupling constant $g_{\pi }$. While the pp A_y data favor $g_{\pi }^2/4\pi \le 13.6$, the np A_y data and the deuteron quadrupole moment imply $g_{\pi }^2/4\pi \ge 14.0$. The two diverging values could be reconciled by the assumption of (substantial) charge-splitting of $g_{\pi }$. However, the established theoretical explanation of the charge-dependence of the ${}^1{S}_0$ scattering length (based upon pion mass splitting) is very sensitive to a difference between $g_{{\pi }^0}$ and $g_{{\pi }^{\pm }}$ and rules out any substantial charge-splitting of $g_{\pi }$. Thus, there are real and large discrepancies between the values for $g_{\pi }$ extracted from different NN observables. Future work that could resolve the problems is suggested.

Latex, 19 pages, 4 figures; invited talk presented at the Workshop on `Critical Points in the Determination of the Pion-Nucleon Coupling Constant', Uppsala (Sweden), June 7-8, 1999

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