for studying such a propagator structure, the issue of how to associate the mass eigenstates with the $n$ poles of the propagator matrix becomes fully apparent only from the $(3\times 3)$ case onwards. The case of $(3\times 3)$ mixing captures all relevant aspects of the pole structure and permutation of the states so that the conclusions can be generalised for larger mixing systems.

For illustration and definiteness we use in this paper the language and the formalism of the neutral Higgs sector of the MSSM with ${\mathcal{CP}}$-violating mixing, i.e. for the three lowest-order mass eigenstates $i,j,k = h,H,A$ and their mixing into the loop-corrected mass eigenstates $h_a,~a=1,2,3$. Since the analytic discussions in Chapters \[sect:LoopMix\]-\[sect:fullBWZ\] do not rely on any model-dependent relations of the MSSM, the results can be transferred also to scalar sectors of other models by replacing $h,H,A$ by a different set of $i,j,k$, and analogously $h_a$ by a general $X_a$, where the generalisation to the case of mixing among more than three particles should be straightforward. Upon incorporation of the appropriate spin structure, the results can also be generalised to the case of mixing propagators of vector bosons or fermions.

The Higgs propagators in the MSSM in fact 