Quantum loop groups for symmetric Cartan matrices

We introduce a quantum loop group associated to a general symmetric Cartan matrix, by imposing just enough relations between the usual generators $\{e_{i,k},f_{i,k}{\}}_{i\in I,k\in \mathbb{Z}}$ in order for the natural Hopf pairing between the positive and negative halves of the quantum loop group to be perfect. As an application, we describe the localized K-theoretic Hall algebra of any quiver without loops, endowed with a particularly important ${\mathbb{C}}^{\ast }$ action.