Hamiltonian type operators in representations of the quantum algebra U_q(su_1,1)

Abstract:
We study some classes of symmetric operators for the discrete series representations of the quantum algebra U_q(su_1,1), which may serve as Hamiltonians of various physical systems. The problem of diagonalization of these operators (eigenfunctions, spectra, overlap coefficients, etc.) is solved by expressing their overlap coefficients in terms of the known families of q-orthogonal polynomials. We consider both bounded and unbounded operators. In the latter case they are not selfadjoint and have deficiency indices (1,1), which means that they may have infinitely many selfadjoint extensions. We find possible sets of point spectrum for one of such operators by using the orthogonality relations for q-Laguerre polynomials. In the other case, we are led to q-orthogonal polynomials related to the Al-Salam-Chihara polynomials. Many new realizations for the discrete series representations are constructed, which follow from the diagonalization of the operators considered.