Spectral equivalences from Bethe Ansatz equations

The one-dimensional Schrödinger equation for the potential x + αx + l(l+ 1)/x has many interesting properties. For certain values of the parameters l and α the equation is in turn supersymmetric (Witten), quasi-exactly solvable (Turbiner), and it also appears in Lipatov’s approach to high energy QCD. In this paper we signal some further curious features of these theories, namely novel spectral equivalences with particular secondand third-order differential equations. These relationships are obtained via a recently-observed connection between the theories of ordinary differential equations and integrable models. Generalised supersymmetry transformations acting at the quasi-exactly solvable points are also pointed out, and an efficient numerical procedure for the study of these and related problems is described. Finally we generalise slightly and then prove a conjecture due to Bessis, Zinn-Justin, Bender and Boettcher, concerning the reality of the spectra of certain PT -symmetric quantum-mechanical systems. 1 [email protected] 2 [email protected] [email protected]