Thomas--Wigner rotation as a holonomy for spin-$1/2$ particles

The Thomas--Wigner rotation (TWR) results from the fact that a combination of boosts leads to a non-trivial rotation of a physical system. Its origin lies in the structure of the Lorentz group. In this article we discuss the idea that the TWR can be understood in the geometric manner, being caused by the non-trivially curved relativistic momentum space, i.e. the mass shell, seen as a Riemannian manifold. We show explicitly how the TWR for a massive spin-$1/2$ particle can be calculated as a holonomy of the mass shell. To reach this conclusion we recall how to construct the spin bundle over the mass shell manifold.