  We theoretically investigate current-induced magnetization dynamics in
chiral-lattice helimagnets. Spin-orbit coupling in non-centrosymmetric crystals
induces a reactive spin-transfer torque that has not been previously
considered. We demonstrate how the torque is governed by the crystal symmetry
and acts as an effective magnetic field along the current direction in cubic
B20-type crystals. The effects of the new torque are computed for
current-induced dynamics of spin-spirals and the Doppler shift of spin waves.
In current-induced spin-spiral motion, the new torque tilts the spiral
structure. The spin waves of the spiral structure are initially displaced by
the new torque, while the dispersion relation is unaffected.
