Quasi-exactly solvable extensions of the Kepler-Coulomb potential on the sphere

Abstract

We consider a family of extensions of the Kepler-Coulomb potential on a $d$-dimensional sphere and analyze it in a deformed supersymmetric framework, wherein the starting potential is known to exhibit a deformed shape invariance property. We show that the members of the extended family are also endowed with such a property, provided some constraint conditions relating the potential parameters are satisfied, in other words they are conditionally deformed shape invariant. Since, in the second step of the construction of a partner potential hierarchy, the constraint conditions change, we impose compatibility conditions between the two sets to build quasi-exactly solvable potentials with known ground and first-excited states. Some explicit results are obtained for the first three members of the family. We then use a generating function method, wherein the first two superpotentials, the first two partner potentials, and the first two eigenstates of the starting potential are built from some generating function $W_+(r)$ [and its accompanying function $W_-(r)$]. From the results obtained for the latter for the first three family members, we propose some formulas for $W_{\pm}(r)$ valid for the $m$th family member, depending on $m+1$ constants $a_0$, $a_1$, \ldots, $a_m$. Such constants satisfy a system of $m+1$ linear equations. Solving the latter allows us to extend the results up to the seventh family member and then to formulate a conjecture giving the general structure of the $a_i$ constants in terms of the parameters of the problem.