Simply-laced root systems arising from quantum affine algebras

Let $U_q'(\mathfrak{g})$ be a quantum affine algebra with an indeterminate $q$ and let $\mathscr{C}_{\mathfrak{g}}$ be the category of finite-dimensional integrable $U_q'(\mathfrak{g})$-modules. We write $\mathscr{C}_{\mathfrak{g}}^0$ for the monoidal subcategory of $\mathscr{C}_{\mathfrak{g}}$ introduced by Hernandez-Leclerc. In this paper, we associate a simply-laced finite type root system to each quantum affine algebra $U_q'(\mathfrak{g})$ in a natural way, and show that the block decompositions of $\mathscr{C}_{\mathfrak{g}}$ and $\mathscr{C}_{\mathfrak{g}}^0$ are parameterized by the lattices associated with the root system. We first define a certain abelian group $\mathcal{W}$ (resp. $\mathcal{W}_0$) arising from simple modules of $\mathscr{C}_{\mathfrak{g}}$ (resp. $\mathscr{C}_{\mathfrak{g}}^0$) by using the invariant $\Lambda^\infty$ introduced in the previous work by the authors. The groups $\mathcal{W}$ and $\mathcal{W}_0$ have the subsets $\Delta$ and $\Delta_0$ determined by the fundamental representations in $\mathscr{C}_{\mathfrak{g}}$ and $\mathscr{C}_{\mathfrak{g}}^0$ respectively. We prove that the pair $( \mathbb{R} \otimes_\mathbb{Z} \mathcal{W}_0, \Delta_0)$ is an irreducible simply-laced root system of finite type and the pair $( \mathbb{R} \otimes_\mathbb{Z} \mathcal{W}, \Delta)$ is isomorphic to the direct sum of infinite copies of $( \mathbb{R} \otimes_\mathbb{Z} \mathcal{W}_0, \Delta_0)$ as a root system.