# Order-dependent mappings: Strong-coupling behavior from weak-coupling expansions in non-Hermitian theories

Abstract : A long time ago, it has been conjectured that a Hamiltonian with a potential of the form $x^2$ + $ivx^3$ , $v$ real, has a real spectrum. This conjecture has been generalized to a class of so-called $\mathscr{P}{T}$ symmetric Hamiltonians and some proofs have been given. Here, we show by numerical investigation that the divergent perturbation series can be summed efficiently by an order-dependent mapping (ODM) in the whole complex plane of the coupling parameter $v^2$ , and that some information about the location of level crossing singularities can be obtained in this way. Furthermore, we discuss to which accuracy the strong-coupling limit can be obtained from the initially weak-coupling perturbative expansion, by the ODM summation method. The basic idea of the ODM summation method is the notion of order-dependent "local" disk of convergence and analytic continuation by an order-dependent mapping of the domain of analyticity augmented by the local disk of convergence onto a circle. In the limit of vanishing local radius of convergence, which is the limit of high transformation order, convergence is demonstrated both by numerical evidence as well as by analytic estimates.
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Jean Zinn-Justin, Ulrich D. Jentschura. Order-dependent mappings: Strong-coupling behavior from weak-coupling expansions in non-Hermitian theories. Journal of Mathematical Physics, American Institute of Physics (AIP), 2010, 51 (7), pp.072106. ⟨10.1063/1.3451104⟩. ⟨cea-02895258⟩

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