Global dimension function on stability conditions and Gepner equations

We study the global dimension function $\operatorname{gldim}\colon\operatorname{Aut}\backslash\operatorname{Stab}\mathcal{D}/\mathbb{C}\to\mathbb{R}_{\ge0}$ on a quotient of the space of Bridgeland stability conditions on a triangulated category $\mathcal{D}$ as well as Toda's Gepner equatio $\Phi(\sigma)=s\cdot\sigma$ for some $\sigma\in\operatorname{Stab}\mathcal{D}$ and $(\Phi,s)\in\operatorname{Aut}\mathcal{D}\times\mathbb{C}$. For the bounded derived category $\mathcal{D}^b(\mathbf{k} Q)$ of a Dynkin quiver $Q$, we show that there is a unique minimal point $\sigma_G$ of $\operatorname{gldim}$ (up to the $\mathbb{C}$-action), with value $1-2/h$, which is the solution of the Gepner equation $\tau(\sigma)=(-2/h)\cdot\sigma$. Here $\tau$ is the Auslander-Reiten functor and $h$ is the Coxeter number. This solution $\sigma_G$ was constructed by Kajiura-Saito-Takahashi. We also show that for an acyclic non-Dynkin quiver $Q$, the minimal value of $\operatorname{gldim}$ is $1$. Our philosophy is that the infimum of $\operatorname{gldim}$ on $\operatorname{Stab}\mathcal{D}$ is the global dimension for the triangulated category $\mathcal{D}$. We explain how this notion could shed light on the contractibility conjecture of the space of stability conditions.