Trigonometric K-matrices for finite-dimensional representations of quantum affine algebras

Abstract: Let $\mathfrak{g}$ be a complex simple Lie algebra and $U_q\hat{\mathfrak{g}}$ the corresponding quantum affine algebra. We prove that every irreducible finite-dimensional $U_q\hat{\mathfrak{g}}$-module gives rise to a family of trigonometric K-matrices, i.e., rational solutions of Cherednik's generalized reflection equation. The result depends upon the choice of a quantum affine symmetric pair $U_q\mathfrak{k}\subset U_q\hat{\mathfrak{g}}$. It hinges on the construction of universal K-matrices for arbitrary quantum symmetric pairs, and relies on proving that every irreducible $U_q\hat{\mathfrak{g}}$-module is generically irreducible under restriction to $U_q{\mathfrak{k}}$. In the case of small modules and Kirillov-Reshetikhin modules, we obtain new solutions of the standard and the transposed reflection equations.