  We consider the two-nucleon weak interaction with a pionless effective field
theory. Dibaryon fields are introduced to facilitate calculations and ensure
precision in the initial and final state propagators. Weak interactions are
accounted for with the parity-violating dibaryon-nucleon-nucleon vertices,
which contain unknown weak dibaryon-nucleon-nucleon coupling constants. We
apply the model to the calculation of a parity-violating observable in the
neutron-proton capture at threshold. Result is obtained up to the linear order
in the unknown dibaryon-nucleon-nucleon coupling constants. We compare our
result to the one obtained from a hybrid calculation, and discuss the extension
to weak interactions in the few-body systems.
