Generalized cluster structures on $\mathrm{SL}_n^\dagger$ (2312.04859v1)

Abstract: We study Poisson varieties $(\mathrm{SL}n^{\dagger},\pi{\mathbf{\Gamma}}^{\dagger})$ parameterized by Belavin-Drinfeld triples $\mathbf{\Gamma}$ of type $A_{n-1}$ along with generalized cluster structures $\mathcal{GC}^{\dagger}(\mathbf{\Gamma})$ on $\mathrm{SL}n^{\dagger}$ compatible with $\pi{\mathbf{\Gamma}}^{\dagger}$. As a variety, $\mathrm{SL}n^{\dagger}$ is a Zariski open subset of $\mathrm{SL}_n$ obtained as the image of the dual Poisson-Lie group $(\mathrm{SL}_n^{*},\pi{\mathbf{\Gamma}}^*)$ of $(\mathrm{SL}n,\pi{\mathbf{\Gamma}})$ under a certain rational map. We prove that the generalized upper cluster structure of $\mathcal{GC}^{\dagger}(\mathbf{\Gamma})$ on $\mathrm{SL}n$ is naturally isomorphic to $\mathcal{O}(\mathrm{SL}_n)$. Moreover, for any connected reductive complex group $G$ and a BD triple $\mathbf{\Gamma}$, we produce a rational map $\mathcal{Q}:(G,\pi{\text{std}}^{\dagger})\dashrightarrow(G,\pi_{\mathbf{\Gamma}}^{\dagger})$ that is a Poisson isomorphism if the $r_0$ parts of $\pi_{\text{std}}^{\dagger}$ and $\pi_{\mathbf{\Gamma}}^{\dagger}$ coincide; furthermore, in the case when $G \in {\mathrm{SL}n,\mathrm{GL}_n}$, we show that $\mathcal{Q}$ is a birational quasi-isomorphism between $\mathcal{GC}^\dagger(\mathbf{\Gamma}{\text{std}})$ and $\mathcal{GC}^\dagger(\mathbf{\Gamma})$. Lastly, for any pair of BD triples $\tilde{\mathbf{\Gamma}} \prec \mathbf{\Gamma}$ of type $A_{n-1}$ comparable in the natural order, we use the map $\mathcal{Q}$ to construct a birational quasi-isomorphism between $\mathcal{GC}^{\dagger}(\tilde{\mathbf{\Gamma}})$ and $\mathcal{GC}^{\dagger}(\mathbf{\Gamma})$.