Bethe Ansatz and the Spectral Theory of affine Lie algebra-valued connections I. The simply-laced case

Abstract: We study the ODE/IM correspondence for ODE associated to $\hat{\mathfrak g}$-valued connections, for a simply-laced Lie algebra $\mathfrak g$. We prove that subdominant solutions to the ODE defined in different fundamental representations satisfy a set of quadratic equations called $\Psi$-system. This allows us to show that the generalized spectral determinants satisfy the Bethe Ansatz equations.