Momentum bispinor, two-qubit entanglement and twistor space

We re-examine the symmetry structure of massive momentum bispinors in four dimensional Minkowski spacetime and apply the result to the geometry of a two-qubit entanglement system. The geometry of entanglement is recovered by restricting the momentum to unit-energy hyperplane inside the future light-cone. On a more formal side, to understand Czachor's alternative normalization of the bispinor and its projection property, we analyze the geometry of momentum twistor space. An interesting correpondence between a submanifold of the momentum twistor space and tachyonic particle is also investigated.