  We analyze the power counting of two-body currents in nuclear effective field
theories (EFTs). We find that the existence of non-perturbative physics at low
energies, which is manifest in the existence of the deuteron and the 1S0 NN
virtual bound state, combined with the appearance of singular potentials in
versions of nuclear EFT that incorporate chiral symmetry, modifies the
renormalization-group flow of the couplings associated with contact operators
that involve nucleon-nucleon pairs and external fields. The order of these
couplings is thereby enhanced with respect to the naive-dimensional-analysis
estimate. Consequently, short-range currents enter at a lower order in the
chiral EFT than has been appreciated up until now, and their impact on
low-energy observables is concomitantly larger. We illustrate the changes in
the power counting with a few low-energy processes involving external probes
and the few-nucleon systems, including electron-deuteron elastic scattering and
radiative neutron capture by protons.
