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

The deuteron, NN analyzing powers A_y, and the singlet scattering length show great sensitivity to the $πNN$ coupling constant $g_π$. While the pp A_y data favor $g^2_π/4π\leq 13.6$, the np A_y data and the deuteron quadrupole moment imply $g^2_π/4π\geq 14.0$. The two diverging values could be reconciled by the assumption of (substantial) charge-splitting of $g_π$. However, the established theoretical explanation of the charge-dependence of the $^1S_0$ scattering length (based upon pion mass splitting) is very sensitive to a difference between $g_{π^0}$ and $g_{π^\pm}$ and rules out any substantial charge-splitting of $g_π$. Thus, there are real and large discrepancies between the values for $g_π$ extracted from different NN observables. Future work that could resolve the problems is suggested.

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