  We show that chiral effective field theory (EFT) two-body currents provide
important contributions to the quenching of low-momentum-transfer Gamow-Teller
transitions, and use chiral EFT to predict the momentum-transfer dependence
that is probed in neutrinoless double-beta decay. We then calculate for the
first time the neutrinoless double-beta decay operator based on chiral EFT
currents and study the nuclear matrix elements at successive orders. The
contributions from chiral two-body currents are significant and should be
included in all calculations.
