Chiral effective field theory analysis of hadronic parity violation in few-nucleon systems

Background: Weak interactions between quarks induce a parity-violating (PV) component in the nucleon-nucleon potential, whose effects are currently being studied in a number of experiments involving few-nucleon systems. In the present work, we reconsider the derivation of this PV component within a chiral effective field theory (χEFT) framework. Purpose: The objectives of the present work are twofold. The first is to perform a detailed analysis of the PV nucleon-nucleon potential up to next-to-next-to-leading (N2LO) order in the chiral expansion, in particular, by determining the number of independent low-energy constants (LECs) at N2LO. The second objective is to investigate PV effects in a number of few-nucleon observables, including the p - -p longitudinal asymmetry, the neutron spin rotation in n - -p and n - -d scattering, and the longitudinal asymmetry in the 3He(n - ,p)3H charge-exchange reaction. Methods: The χEFT PV potential includes one-pion-exchange, two-pion-exchange, and contact terms as well as 1/M (M being the nucleon mass) nonstatic corrections. Dimensional regularization is used to renormalize pion loops. The wave functions for the A=2-4 nuclei are obtained by using strong two- and three-body potentials also derived, for consistency, from χEFT. In the case of the A=3-4 systems, the wave functions are computed by expanding on a hyperspherical harmonics functions basis. Results: We find that the PV potential at N2LO depends on six LECs: the pion-nucleon PV coupling constant hπ1 and five parameters multiplying contact interactions. An estimate for the range of values of the various LECs is provided by using available experimental data, and these values are used to obtain predictions for the other PV observables. Conclusions: The χEFT approach provides a very satisfactory framework to analyze PV effects in few-nucleon systems.