  Two-nucleon axial charge and current operators are derived in chiral
effective field theory up to one loop. The derivation is based on time-ordered
perturbation theory, and accounts for cancellations between the contributions
of irreducible diagrams and the contributions due to non-static corrections
from energy denominators of reducible diagrams. Ultraviolet divergencies
associated with the loop corrections are isolated in dimensional
regularization. The resulting axial current is finite and conserved in the
chiral limit, while the axial charge requires renormalization. A complete set
of contact terms for the axial charge up to the relevant order in the power
counting is constructed.
