Inhomogeneous $q$-Whittaker Polynomials I: Duality and Expansions

Abstract: We introduce a new family of symmetric polynomials $\mathfrak{G}^{(\mathbf{u},\mathbf{v})}_λ$ arising from exactly solvable lattice models associated with the quantised loop algebra $\mathcal{U}{q}(\mathfrak{sl}{2}[z^\pm])$. The polynomials $\mathfrak{G}^{(\mathbf{u},\mathbf{v})}_λ$ unify $q$-Whittaker polynomials, inhomogeneous $q$-Whittaker polynomials, Grothendieck polynomials and their duals. Using Yang--Baxter equation, we derive Cauchy identities and combinatorial formulas for the transition coefficients.