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arXiv · 1802.02902

Quasi-exactly solvable Schr\"odinger equations, symmetric polynomials, and functional Bethe ansatz method

C. Quesne
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Abstract

For applications to quasi-exactly solvable Schr\"odinger equations in quantum mechanics, we consider the general conditions that have to be satisfied by the coefficients of a second-order differential equation with at most $k+1$ singular points in order that this equation has particular solutions that are $n$th-degree polynomials. In a first approach, we show that such conditions involve $k-2$ integration constants, which satisfy a system of linear equations whose coefficients can be written in terms of elementary symmetric polynomials in the polynomial solution roots whenver such roots are all real and distinct. In a second approach, we consider the functional Bethe ansatz method in its most general form under the same assumption. Comparing the two approaches, we prove that the above-mentioned $k-2$ integration constants can be expressed as linear combinations of monomial symmetric polynomials in the roots, associated with partitions into no more than two parts. We illustrate these results by considering a quasi-exactly solvable extension of the Mathews-Lakshmanan nonlinear oscillator corresponding to $k=4$.

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C. Quesne. 2018-02-07. Quasi-exactly solvable Schr\"odinger equations, symmetric polynomials, and functional Bethe ansatz method. https://arxiv.org/abs/1802.02902

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