Foldy–Wouthuysen representation in standard model of electroweak interaction

The Hamiltonian operator in the Foldy–Wouthuysen representation describing the electroweak interaction of relativistic spin-$1/2$ particles in the standard model is obtained. The weak interaction caused by neutral currents is studied. The operator equation describing the particle spin motion in electroweak field is found. The parity nonconservation in heavy atoms is considered.