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Journal of Lie Theory 33 (2023), No. 1, 029--077
Copyright Heldermann Verlag 2023

Askey-Wilson Polynomials and Branching Laws

Allen Back
Department of Mathematics, Malott Hall, Cornell University, Ithaca, U.S.A.

Birgit Speh
Department of Mathematics, Malott Hall, Cornell University, Ithaca, U.S.A.

Bent Oersted
Dept. of Mathematics, Aarhus University, Denmark

Siddhartha Sahi
Department of Mathematics, Rutgers University, New Brunswick, U.S.A.

Connection coefficient formulas for special functions describe change of basis matrices under a parameter change, for bases formed by the special functions. Such formulas are related to branching questions in representation theory. The Askey-Wilson polynomials are one of the most general 1-variable special functions. Our main results are connection coefficient formulas for shifting one of the parameters of the nonsymmetric Askey-Wilson polynomials. We also show how one of these results can be used to re-prove an old result of Askey and Wilson in the symmetric case. The method of proof combines establishing a simpler special case of shifting one parameter by a factor of q with using a co-cycle condition property of the transition matrices involved. Supporting computations use the Noumi representation and are based on simple formulas for how some basic Hecke algebra elements act on natural "almost symmetric" Laurent polynomials.

Keywords: Connection coefficients, branching, DAHA, Askey-Wilson polynomials, spherical functions.

MSC: 33D67, 22E47, 33D45, 17B37.

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