## Classical and quantum integrable systems in $$\widetilde{\mathfrak gl}(2)^{+*}$$ and separation of variables.(English)Zbl 0842.58046

Summary: Classical integrable Hamiltonian systems generated by elements of the Poisson commuting ring of spectral invariants on rational coadjoint orbits of the loop algebra $$\widetilde {{\mathfrak g}{\mathfrak l}}^{+*} (2, \mathbb{R})$$ are integrated by separation of variables in the Hamilton-Jacobi equation in hyperellipsoidal coordinates. The canonically quantized systems are then shown to also be completely integrable and separable within the same coordinates. Pairs of second class constraints defining reduced phase spaces are implemented in the quantized systems by choosing one constraint as an invariant, and interpreting the other as determining a quotient (i.e. by treating one as a first class constraint and the other as a gauge condition). Completely integrable, separable systems on spheres and ellipsoids result, but those on ellipsoids require a further modification of order $$O(\hbar^2)$$ in the commuting invariants in order to assure self-adjointness and to recover the Laplacian for the case of free motion. For each case – in the ambient space $$\mathbb{R}^n$$, the sphere and the ellipsoid – the Schrödinger equations are completely separated in hyperellipsoidal coordinates, giving equations of generalized Lamé type.

### MSC:

 37J35 Completely integrable finite-dimensional Hamiltonian systems, integration methods, integrability tests 37K10 Completely integrable infinite-dimensional Hamiltonian and Lagrangian systems, integration methods, integrability tests, integrable hierarchies (KdV, KP, Toda, etc.) 35Q40 PDEs in connection with quantum mechanics 53D50 Geometric quantization 35Q58 Other completely integrable PDE (MSC2000)
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