Factorization Method in Curvilinear Coordinates and Pairing of Levels   for Matrix Potentials
  Multidimensional factorization method is formulated in arbitrary curvilinear coordinates. Particular cases of polar and spherical coordinates are considered and matrix potentials with separating variables are constructed. A new class of matrix potentials is obtained which reveals a double degeneracy or equidistant splitting of energy levels (hidden symmetry). 
A.A.Andrianov, M.V.Ioffe and Tsu Zhun-Pin
hep-th math-ph math.MP quant-ph