Extensions of a commuting pair of quantum toroidal $\mathfrak{gl}_1$
B. Feigin, M. Jimbo, E. Mukhin
TL;DR
The paper defines $\mathcal{A}_{M,N}$ as an extension gluing two commuting quantum toroidal $\mathfrak{gl}_1$ algebras $\mathcal{E}_1$ and $\check{\mathcal{E}}_1$ with parameter constraints $M,N$, recovering a shifted $\mathfrak{gl}_2$ structure when $M=\pm1$. It proposes a coproduct $\Delta_{N_1,N_2}$ into a completed tensor product that extends the standard coproduct on the subalgebra, and develops free-field representations, including $\mathbb{F}_{2;2}$ and Wakimoto-like constructions, as well as tensor products with Fock modules and screened intertwiners to realize level-2-type modules $\mathbb{F}_{2,2;2,2}$. The work analyzes automorphisms, gradings, and special cases (notably $(1,0)$ and $(0,0)$) and discusses the challenges and structure of the coproduct, offering concrete examples that corroborate the conjectured coproduct and hint at connections to shifted and deformed $W$-algebras. This framework exposes a rich algebraic-gluing mechanism for quantum toroidal algebras and opens avenues for further quiver and plane-partition-type interpretations.
Abstract
We introduce a family of algebras $\mathcal{A}_{M,N}$, $M,N\in\mathbb{Z}$, as an extension of a pair of commuting quantum toroidal $\mathfrak{gl}_1$ subalgebras $\mathcal{E}_1,\check{\mathcal{E}}_1$, wherein the parameters are tuned in a specific way according to $M,N$. In the case $M=\pm 1$, algebra $\mathcal{A}_{\pm1,N}$ is a shifted quantum toroidal $\mathfrak{gl}_2$ algebra introduced in [FJM2]. Conjecturally there is a coproduct homomorphism $\mathcal{A}_{M,N_1+N_2}\to\mathcal{A}_{M,N_1}\hat\otimes\mathcal{A}_{M,N_2}$ to a completed tensor product, whose restriction to the subalgebras $\mathcal{E}_1,\check{\mathcal{E}}_1$ coincides with the standard coproduct of the latter. We give examples of $\mathcal{A}_{M,N}$ modules constructed on certain direct sums of tensor products of Fock modules of $\mathcal{E}_1\otimes\check{\mathcal{E}}_1$.
