Parity-violating three-nucleon interactions at low energies and large NC

Abstract

The parity-violating (PV) nucleon-nucleon ($N\!N$) interaction in the three-nucleon system is investigated using pionless effective field theory ($\mathrm{EFT}(/\!\!\!\pi)$). This work shows that a next-to-leading order (NLO) PV three-body force is necessary in contradiction with a previous claim [Griesshammer and Schindler in Eur. Phys. J. A 46, 73 (2010)]. Including three-body $P$ to $D$-wave transitions PV three-nucleon observables are calculated to higher energies than previously considered. Using the recent large-$N_{C}$ analysis of the PV $N\!N$ interaction in $\mathrm{EFT}(/\!\!\!\pi)$ the current understanding of low energy PV few-body measurements is reassessed. The recent measurement of the asymmetry $A_{\gamma}$ in $\vec{n}p\to d\gamma$ from the NPDGamma collaboration [D. Blyth et al. (NPDGamma), Phys. Rev. Lett. 121, 242002 (2018)], gives the value $g_{4}^{(N_{C}^{-1})}=(-1.4\pm 0.63(stat.)\pm 0.09(syst.))\times 10^{-10}~\mathrm{MeV}^{-1}$ for a next-to-next-to-leading order (N$^{2}$LO) in large-$N_{C}$ low energy constant (LEC). Using the large-$N_{C}$ hierarchy of LECs the sizes of the leading order (LO) in large-$N_{C}$ LECs are estimated using an experimental bound on a parity violating asymmetry in $\vec{p}d$ scattering at $E_{\mathrm{lab}}=15$ MeV and a measurement of $\vec{pp}$ scattering at $E_{\mathrm{lab}}=13.6$ MeV. Comparing the size of the resulting LO in large-$N_{C}$ LECs to the N$^{2}$LO in large-$N_{C}$ LEC $g_{4}^{(N_{C}^{-1})}$ shows they are roughly the same size in contradiction with current large-$N_{C}$ counting.