Systematics of quasi-Hermitian representations of non-Hermitian quantum models

In the currently quickly growing area of applications of non -Hermitian Hamiltonians H not equal H-dagger which are quasi-Hermitian (i.e., such that H-dagger Theta not equal Theta H, with a suitable inner-product metric Theta not equal I), the correct probabilistic interpretation of the model is needed. Achieved either in the Buslaev-Grecchi-inspired spirit (BGI; one factorizes Theta = Omega dagger Omega and reconstructs the conventional Her-mitian Hamiltonian, H -> gimel = Omega H Omega(-1) = gimel(dagger)) or in the much user-friendlier, Dyson-inspired spirit (DI; one eliminates the "dif-ficult"reference to h via the quasi-Hermiticity rule, i.e., via an "easier"reconstruction of Theta). Here, the two model-building BGI and DI recipes are identified as the two extreme special cases of a general correct-interpretation-providing strategy. We show that at any preselected integer N one may make a choice between the BGI extreme and an N-plet of the other, consistent and physical DI-type representations of the system in which a specific, partially modified Hamiltonian is constructed as quasi -Hermitian with respect to a specific, simplified inner-product metric. In applications, any one of these N+1 options may prove optimal for a given H: A schematic three-state quantum system is discussed as an illustrative example.(c) 2022 Elsevier Inc. All rights reserved.