  The coupled spin tube system, which is equivalent to a stacked
Kagome-triangular spin system, exhibits the cuboc order -- a non-coplanar spin
order with a twelve-sublattice structure accompanying spontaneous breaking of
the translational symmetry -- in the Kagome-triangular plane. On the basis of
the spin-wave theory, we analyze spin-wave excitations of the planar
Kagome-triangular spin system, where the geometric phase characteristic to the
cuboc spin structure emerges. We further investigate spin-wave excitations and
dynamical spin structure factors for the coupled spin tubes, assuming the
staggered cuboc order.
