D. Kusnezov, INCOMPLETENESS OF REPRESENTATION-THEORY - HIDDEN SYMMETRIES AND QUANTUM NONINTEGRABILITY, Physical review letters, 79(4), 1997, pp. 537-540
Representation theory is shown to be incomplete in terms of enumeratin
g all integrable limits of quantum systems. As a consequence, one can
find exactly solvable Hamiltonians which have apparently strongly brok
en symmetry. The number of these hidden symmetries depends upon the re
alization of the Hamiltonian.