The matrix elements of irreducible representations of ${SU}(2)\times{SU}(2)$ in a diag$({SU}(2)\times{SU}(2))$-basis are expressed in terms of vector-valued orthogonal polynomials, which generalize the Jacobi polynomials.

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SIAM Journal on Mathematical Analysis

Koornwinder, T. H. (1985). Matrix elements of irreducible representations of ${SU}(2)\times{SU}(2)$ and vector-valued orthogonal polynomials. SIAM Journal on Mathematical Analysis, 16(3), 602–613.