Published online by Cambridge University Press: 08 February 2022
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 and 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
$\mathcal {W}$ (respectively
$\mathcal {W} _0$) arising from simple modules of
$\mathscr {C}_{\mathfrak {g}}$ (respectively
$\mathscr {C}_{\mathfrak {g}}^0$) by using the invariant
$\Lambda ^\infty$ introduced in previous work by the authors. The groups
$\mathcal {W}$ and
$\mathcal {W} _0$ have 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
$( \mathbb {R} \otimes _\mathbb {\mspace {1mu}Z\mspace {1mu}} \mathcal {W} _0, \Delta _0)$ is an irreducible simply laced root system of finite type and that the pair
$( \mathbb {R} \otimes _\mathbb {\mspace {1mu}Z\mspace {1mu}} \mathcal {W} , \Delta )$ is isomorphic to the direct sum of infinite copies of
$( \mathbb {R} \otimes _\mathbb {\mspace {1mu}Z\mspace {1mu}} \mathcal {W} _0, \Delta _0)$ as a root system.
The research of M. Kashiwara was supported by Grant-in-Aid for Scientific Research (B) 20H01795 from the Japan Society for the Promotion of Science.
The research of M. Kim was supported by a National Research Foundation (NRF) grant funded by the government of Korea (MSIP) (NRF-2017R1C1B2007824 and NRF-2020R1A5A1016126).
The research of S.-J.O. was supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea (NRF-2019R1A2C4069647).
The research of E.P. was supported by a National Research Foundation (NRF) grant funded by the government of Korea (MSIP)(NRF-2020R1F1A1A01065992 and NRF-2020R1A5A1016126).
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