  Neutron-antineutron ($n-\bar n$) oscillations in the deuteron are considered.
Specifically, the deuteron lifetime is calculated in terms of the free-space
$n-\bar n$ oscillation time $\tau_{n-\bar n}$ based on $NN$ and $\bar NN$
interactions derived within chiral effective field theory (EFT). This results
in $(2.6\pm 0.1) \times 10^{22}\,\tau^2_{n-\bar n}$ s, which is close to the
value obtained by Dover and collaborators more than three decades ago, but
disagrees with recent EFT calculations that were performed within the
perturbative scheme proposed by Kaplan, Savage, and Wise. Possible reasons for
the difference are discussed.
