On the stratifications of 2-qubits X-state space

The 7-dimensional family $mathfrak{P}_X$ of so-called mixed X-states of 2-qubits is considered. Two types of stratification of 2-qubits $X-$state space, i.e., partitions of $mathfrak{P}_X,$ into orbit types with respect to the adjoint group actions, one of the global unitary group $G_X subset SU(4)$ and another one under the action of the local unitary group $LG_X subset G_X$, is described. The equations and inequalities in the invariants of the corresponding groups, determining each stratification component, are given.