Orthogonality of spin $q$-Whittaker polynomials
Matteo Mucciconi
TL;DR
This work proves that the inhomogeneous spin $q$-Whittaker polynomials $\mathbb{f}_\lambda(\boldsymbol{x}_n|\boldsymbol{a}_{n-1},\boldsymbol{b}_{n-1})$ are self-orthogonal under a torus Sklyanin-type measure and hence form a basis for the space of symmetric polynomials in $n$ variables, with an explicit norm $\mathsf{c}_n(\lambda|\boldsymbol{a}_{n-1},\boldsymbol{b}_{n-1})$. The authors also show that the related family $\mathbb{F}_\lambda(\boldsymbol{x}_n|\boldsymbol{a}_{n},\boldsymbol{b}_{n})$ is a basis, connecting to vanishing-condition characterizations and specializations to spin Grothendieck polynomials, interpolation $q$-Whittaker polynomials, and spin Whittaker functions. Central to the results are inhomogeneous eigenrelations, Cauchy-type identities, and a carefully constructed torus scalar product that generalizes the classical $q$-Whittaker orthogonality. The paper further discusses special cases and formal limits, highlighting links to integrable probabilistic models and potential representation-theoretic interpretations of the orthogonality in the Grothendieck and Whittaker regimes. Overall, the results establish completeness and orthogonality in a rich, multi-parameter setting, providing tools for both algebraic and probabilistic applications in the theory of symmetric functions.
Abstract
The inhomogeneous spin $q$-Whittaker polynomials are a family of symmetric polynomials which generalize the Macdonald polynomials at $t=0$. In this paper we prove that they are orthogonal with respect to a variant of the Sklyanin measure on the $n$ dimensional torus and as a result they form a basis of the space of symmetric polynomials in $n$ variables. Instrumental to the proof are inhomogeneous eigenrelations, which partially generalize those of Macdonald polynomials. We also consider several special cases of the inhomogeneous spin $q$-Whittaker polynomials, which include variants of symmetric Grothendieck polynomials or spin Whittaker functions.
