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Perturbation method with triangular propagators and anharmonicities of intermediate strength

Miloslav Znojil
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Abstract

I propose a new version of the Rayleigh - Schrödinger perturbation method. It admits a lower triangular matrix in place of the usual diagonal propagator. Illustrated on rational anharmonicities polynomial}(x)/polynomial}(x), treated as perturbations of (quasi-)exact anharmonic oscilators. In this sense the method works in an intermediate-coupling regime and bridges the gap between the weak- and strong-coupling expansions.

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Miloslav Znojil. 1999-10-27. Perturbation method with triangular propagators and anharmonicities of intermediate strength. https://arxiv.org/abs/quant-ph/9910114

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