[De la Double Affinisation Quantique : 1. En type $\mathfrak{a}_1$]
We define the double quantum affinization $\ddot{\mathrm{U}}_q(\mathfrak{a}_1)$ of type $\mathfrak{a}_1$ as a topological Hopf algebra. We prove that it admits a subalgebra $\ddot{\mathrm{U}}_q^{\prime }(\mathfrak{a}_1)$ whose completion is (bicontinuously) isomorphic to the completion of the quantum toroidal algebra $\dot{\mathrm{U}}_q ( \dot{\mathfrak{a}}_1 ) $, defined as the (simple) quantum affinization of the untwisted affine Kač–Moody Lie algebra $\dot{\mathfrak{sl}}_2$ of type $\dot{\mathfrak{a}}_1$, equipped with a certain topology inherited from its natural $\mathbb{Z}$-grading. The isomorphism is constructed by means of a bicontinuous action by automorphisms of an affinized version $\ddot{\mathfrak{B}}$ – technically a split extension $\ddot{\mathfrak{B}}\cong \dot{\mathfrak{B}} \ltimes P^\vee $ by the coweight lattice $P^\vee $ – of the affine braid group $\dot{\mathfrak{B}}$ of type $\dot{\mathfrak{a}}_1$ on that completion of $\dot{\mathrm{U}}_q ( \dot{\mathfrak{a}}_1 ) $. It can be regarded as an affinized version of the Damiani–Beck isomorphism, familiar from the quantum affine setting. We eventually prove the corresponding triangular decomposition of $\ddot{\mathrm{U}}_q(\mathfrak{a}_1)$ and briefly discuss the consequences regarding the representation theory of quantum toroidal algebras.
Nous définissons la double affinisation quantique $\ddot{\mathrm{U}}_q(\mathfrak{a}_1)$ de type $\mathfrak{a}_1$ comme une algèbre de Hopf topologique. Nous démontrons qu’elle admet une sous-algèbre $\ddot{\mathrm{U}}_q^{\prime }(\mathfrak{a}_1)$ dont la complétion est (bicontinûment) isomorphe à la complétion de l’algèbre quantique toroïdale $\dot{\mathrm{U}}_q ( \dot{\mathfrak{a}}_1 ) $, elle-même définie comme l’affinisaton quantique (simple) de l’algèbre de Kač–Moody affine non-torsionnée $\dot{\mathfrak{sl}}_2$ de type $\dot{\mathfrak{a}}_1$, munie d’une certaine topologie héritée de sa $\mathbb{Z}$-graduation naturelle. L’isomorphisme est construit au moyen d’une action bicontinue par automorphismes d’une version affinisée $\ddot{\mathfrak{B}}$ – techniquement une extension scindée $\ddot{\mathfrak{B}}\cong \dot{\mathfrak{B}} \ltimes P^\vee $ par le réseau des co-poids $P^\vee $ – du groupe des tresses affine $\dot{\mathfrak{B}}$ de type $\dot{\mathfrak{a}}_1$ sur cette complétion de $\dot{\mathrm{U}}_q ( \dot{\mathfrak{a}}_1 ) $. Il peut être vu comme une version affinisée de l’isomorphisme de Damiani–Beck, bien connu dans le cadre des algèbres quantiques affines. Nous prouvons finalement la décomposition triangulaire correspondante de $\ddot{\mathrm{U}}_q(\mathfrak{a}_1)$ et discutons brièvement les conséquences sur la théorie des représentations des algèbres quantiques toroïdales.
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Keywords: Quantum Affine Algebras, Quantum Toroidal Algebras, Representation Theory
Mots-clés : Algèbres auantiques affines, algèbres quantiques toroïdales, théorie des représentations
Zegers, Robin 1 ; Mounzer, Elie 1

@article{AIF_2025__75_6_2359_0, author = {Zegers, Robin and Mounzer, Elie}, title = {On double quantum affinization: 1. {Type} $ \mathfrak{a}_1$}, journal = {Annales de l'Institut Fourier}, pages = {2359--2422}, publisher = {Association des Annales de l{\textquoteright}institut Fourier}, volume = {75}, number = {6}, year = {2025}, doi = {10.5802/aif.3691}, language = {en}, url = {https://aif.centre-mersenne.org/articles/10.5802/aif.3691/} }
TY - JOUR AU - Zegers, Robin AU - Mounzer, Elie TI - On double quantum affinization: 1. Type $ \mathfrak{a}_1$ JO - Annales de l'Institut Fourier PY - 2025 SP - 2359 EP - 2422 VL - 75 IS - 6 PB - Association des Annales de l’institut Fourier UR - https://aif.centre-mersenne.org/articles/10.5802/aif.3691/ DO - 10.5802/aif.3691 LA - en ID - AIF_2025__75_6_2359_0 ER -
%0 Journal Article %A Zegers, Robin %A Mounzer, Elie %T On double quantum affinization: 1. Type $ \mathfrak{a}_1$ %J Annales de l'Institut Fourier %D 2025 %P 2359-2422 %V 75 %N 6 %I Association des Annales de l’institut Fourier %U https://aif.centre-mersenne.org/articles/10.5802/aif.3691/ %R 10.5802/aif.3691 %G en %F AIF_2025__75_6_2359_0
Zegers, Robin; Mounzer, Elie. On double quantum affinization: 1. Type $ \mathfrak{a}_1$. Annales de l'Institut Fourier, Tome 75 (2025) no. 6, pp. 2359-2422. doi : 10.5802/aif.3691. https://aif.centre-mersenne.org/articles/10.5802/aif.3691/
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