On Pseudo-Hermitian Hamiltonians

We investigate some questions on the construction of $\eta$ operators for pseudo-Hermitian Hamiltonians. We give a sufficient condition which can be exploited to systematically generate a sequence of $\eta$ operators starting from a known one, thereby proving the non-uniqueness of $\eta$ for a particular pseudo-Hermitian Hamiltonian. We also study perturbed Hamiltonians for which $\eta$'s corresponding to the original Hamiltonian still work.