Parity-violating internucleon potential and strong-interaction enhancement

Abstract

The $\mathrm{NN}\ensuremath{\pi}$ and $\mathrm{NNV}$ vertices that enter the parity-violating internucleon potential are calculated in the Cabibbo and Weinberg-Salam models, using a mechanism whereby octet enhancement results from the short-distance behavior of the current-current product. A quark model is used to calculate the $\mathrm{NN}\ensuremath{\pi}$ vertex, and for the $\mathrm{NNV}$ vertices, a modified factorization approach is proposed. The Cabibbo $\mathrm{NN}\ensuremath{\pi}$ vertex is estimated to be an order of magnitude smaller than previous calculations had indicated and arguments against the previous method are given. In the Weinberg model the $\mathrm{NN}\ensuremath{\pi}$ vertex is $A({N}_{\ensuremath{-}}^{0})=1.3{{sin}^{2}\ensuremath{\theta}}_{W}A({\ensuremath{\Lambda}}_{\ensuremath{-}}^{0})$, with only neutral currents contributing. In both models the $\mathrm{NNV}$ vertices have different SU(3) structure than previously found, and are enhanced. However, reasonable values of the enhancement parameters are not expected to be large enough to explain by themselves the large circular polarization measured in $n+p\ensuremath{\rightarrow}d+\ensuremath{\gamma}$.