  The pion-nucleon coupling constants determine the strength of the long-range
nuclear forces and play a fundamental part in our understanding of nuclear
physics. While the charged- and neutral-pion couplings to protons and neutrons
are expected to be very similar, owing to the approximate isospin symmetry of
the strong interaction, the different masses of the up- and down-quarks and
electromagnetic effects may result in their slightly different values. Despite
previous attempts to extract these coupling constants from different systems,
our knowledge of their values is still deficient. In this Letter we present a
precision determination of these fundamental observables with fully controlled
uncertainties from neutron-proton and proton-proton scattering data using
chiral effective field theory. To achieve this goal, we use a novel methodology
based on the Bayesian approach and perform, for the first time, a full-fledged
partial-wave analysis of nucleon-nucleon scattering up to the pion production
threshold in the framework of chiral effective field theory, including a
complete treatment of isospin-breaking effects and our own determination of
mutually consistent data. The resulting values of the pion-nucleon coupling
constants are accurate at the percent level and show no significant charge
dependence. These results mark an important step towards developing a precision
theory of nuclear forces and structure.
