Hadronic parity violation in n p → dγ with effective field theory

Abstract The parity-violating nucleon–nucleon ( NN ) potential is considered up to next-to-next-to leading order in heavy-baryon chiral perturbation theory. We include one-pion exchange at leading order and the two-pion exchange and two-nucleon contact terms at next-to-next-to-leading order. The effects of intermediate (two-pion exchange) and short-range (two-nucleon contact) terms are probed by calculating the photon asymmetry A γ in n → p → d γ employing Siegert's theorem and an accurate phenomenological potential for the parity-conserving NN interaction. We explore in detail the uncertainties due to the parameters that control the contribution of the short-range interaction. We obtain about 20% uncertainty in the value of A γ up to the next-to-next-to leading order. We discuss the implication of this uncertainty for the determination of the weak pion–nucleon coupling constant and how the uncertainty can be reduced.