  Multi-dimensional nature of core-collapse supernova (CCSN) leads to
asymmetric matter ejection and neutrino emission, that potentially accounts for
the origin of neutron star (NS) kick. Asymmetric neutrino radiation fields are,
in general, accompanied by large-scale inhomogeneous fluid distributions, in
particular for electron-fraction ($Y_e$) distributions. Recently, it has also
been revealed that lower $Y_e$ environments in proto-neutron star envelope can
offer preferable conditions for collective neutrino oscillations. In this
paper, we show that a dipole asymmetry of fast neutrino-flavor conversion
(FFC), one of the collective neutrino oscillation modes, can power a NS kick,
and that it would generate a characteristic correlation between asymmetric
distributions of heavy elements in the ejecta and the direction of NS kick. We
strengthen our argument for the FFC-driven NS kick mechanism by performing
axisymmetric neutrino transport simulations with full Boltzmann neutrino
transport. We show that this mechanism can generate sufficient linear momentum
of neutrinos to account for typical proper motions of NS. Although more
detailed studies are necessary, the present study opens a new channel to give a
natal NS kick.
