Representations of Bound Quivers over $\mathbb{F}_1$ and Hall Algebras

Abstract

Representations of quivers over the virtual field $\mathbb{F}_1$ can be naturally extended to bound quivers with monomial and commutativity relations. In this paper, we introduce and study the Hall algebra $\mathcal{H}_{\mathbb{F}_1}(Q,I)$ for a bound quiver $(Q,I)$ equipped with such relations. As in the quiver setting, $\mathcal{H}_{\mathbb{F}_1}(Q,I)$ is a graded, connected, and cocommutative bialgebra, and the free subgroup generated by all indecomposable representations forms a Lie subalgebra. We study $\mathcal{H}_{\mathbb{F}_1}(Q,I)$ in detail for two special classes of bound quivers: Nakayama bound quivers and gentle one-cycle bound quivers. In both cases, we prove that for any triple $L, M, N$ of $\mathbb{F}_1$-representations over $(Q,I)$, the Hall number $g_{N,L}^M$ coincides with the evaluation of the corresponding Hall polynomial $ϕ_{N,L}^M(t)$ at $t=1$. Consequently, there exists a canonical isomorphism between $\mathcal{H}_{\mathbb{F}_1}(Q,I)$ and the degenerate Hall algebra $\mathcal{H}_1(Q,I)$, justifying Tits's $\mathbb{F}_1$-philosophy in these settings.