qq-Stability conditions via qq-quadratic differentials for Calabi-Yau-X\mathbb{X} categories

We construct a quiver with superpotential $(Q_\mathbf{T},W_\mathbf{T})$ from a marked surface $\mathbf{S}$ with full formal arc system $\mathbf{T}$. Categorically, we show that the associated cluster-$\mathbb{X}$ category is Haiden-Katzarkov-Kontsevich's topological Fukaya category $\mathcal{D}_{\infty}(\mathbf{T})$ of $\mathbf{S}$, which is also an $\mathbb{X}$-baric heart of the Calabi-Yau-$\mathbb{X}$ category $\mathcal{D}_{\mathbb{X}}(\mathbf{T})$ of $(Q_\mathbf{T},W_\mathbf{T})$. Thus stability conditions on $\mathcal{D}_{\infty}(\mathbf{T})$ induces $q$-stability conditions on $\mathcal{D}_{\mathbb{X}}(\mathbf{T})$. Geometrically, we identify the space of $q$-quadratic differentials on the logarithm surface $\log\mathbf{S}_\Delta$, with the space of induced $q$-stability conditions on $\mathcal{D}_{\mathbb{X}}(\mathbf{T})$, with a complex parameter $s$ satisfying $\operatorname{Re}(s)\gg1$. When $s=N$ is an integer, the result gives an $N$-analogue of Bridgeland-Smith's result for realizing stability conditions on the orbit Calabi-Yau-$N$ category $\mathcal{D}_{\mathbb{X}}(\mathbf{T})\mathbin{/\mkern-6mu/}[\mathbb{X}-N]$

qq-Stability conditions on Calabi-Yau-X\mathbb{X} categories and twisted periods

We introduce q-stability conditions $(\sigma,s)$ on Calabi-Yau-$\mathbb{X}$ categories $\mathcal{D}_\mathbb{X}$, where $\sigma$ is a stability condition on $\mathcal{D}_\mathbb{X}$ and $s$ a complex number. Sufficient and necessary conditions are given, for a stability condition on an $\mathbb{X}$-baric heart $\mathcal{D}_\infty$ of $\mathcal{D}_\mathbb{X}$ to $q$-stability conditions on $\mathcal{D}_\mathbb{X}$. As a consequence, we show that the space $\operatorname{QStab}^\oplus\mathcal{D}_\mathbb{X}$ of (induced) open $q$-stability conditions is a complex manifold, whose fibers (fixing $s$) give usual type of spaces of stability conditions. Our motivating examples for $\mathcal{D}_\mathbb{X}$ are coming from Calabi-Yau-$\mathbb{X}$ completions of dg algebras. A geometric application is that, for type $A$ quiver $Q$, the corresponding space $\operatorname{QStab}^\circ_s\mathcal{D}_\mathbb{X}(Q)$ of $q$-stability conditions admits almost Frobenius structure while the central charge $Z_s$ corresponds to the twisted period $P_\nu$, for $\nu=(s-2)/2$, where $s\in\mathbb{C}$ with $\operatorname{Re}(s)\ge2$. A categorical application is that we realize perfect derived categories as cluster(-$\mathbb{X}$) categories for acyclic quiver $Q$. In the sequel, we construct quivers with superpotential from flat surfaces with the corresponding Calabi-Yau-$\mathbb{X}$ categories and realize open/closed $q$-stability conditions as $q$-quadratic differentials.Comment: Updated semistable version, 43 pages, 3 figures. Comments are welcome

C-sortable words as green mutation sequences

Let $Q$ be an acyclic quiver and $\mathbf{s}$ be a sequence with elements in the vertex set $Q_0$. We describe an induced sequence of simple (backward) tilting in the bounded derived category $\mathcal{D}(Q)$, starting from the standard heart $\mathcal{H}_Q=\operatorname{mod}\mathbf{k}Q$ and ending at another heart $\mathcal{H}_\mathbf{s}$ in $\mathcal{D}(Q)$. Then we show that $\mathbf{s}$ is a green mutation sequence if and only if every heart in this simple tilting sequence is greater than or equal to $\mathcal{H}_Q[-1]$; it is maximal if and only if $\mathcal{H}_\mathbf{s}=\mathcal{H}_Q[-1]$. This provides a categorical way to understand green mutations. Further, fix a Coxeter element $c$ in the Coxeter group $W_Q$ of $Q$, which is admissible with respect to the orientation of $Q$. We prove that the sequence $\widetilde{\mathbf{w}}$ induced by a $c$-sortable word $\mathbf{w}$ is a green mutation sequence. As a consequence, we obtain a bijection between $c$-sortable words and finite torsion classes in $\mathcal{H}_Q$. As byproducts, the interpretations of inversions, descents and cover reflections of a $c$-sortable word $\mathbf{w}$ are given in terms of the combinatorics of green mutations.Comment: Last version, to appear in PLM

Frobenius morphisms and stability conditions

We generalize Deng-Du's folding argument, for the bounded derived category $\mathcal{D}(Q)$ of an acyclic quiver $Q$, to the finite dimensional derived category $\mathcal{D}(\Gamma Q)$ of the Ginzburg algebra $\Gamma Q$ associated to $Q$. We show that the $F$-stable category of $\mathcal{D}(\Gamma Q)$ is equivalent to the finite dimensional derived category $\mathcal{D}(\Gamma\mathbb{S})$ of the Ginzburg algebra $\Gamma\mathbb{S}$ associated to the species $\mathbb{S}$, which is folded from $Q$. If $(Q,\mathbb{S})$ is of Dynkin type, we prove that $\operatorname{Stab}\mathcal{D}(\mathbb{S})$ (resp. the principal component $\operatorname{Stab}^\circ\mathcal{D}(\Gamma\mathbb{S})$) of the space of the stability conditions of $\mathcal{D}(\mathbb{S})$ (resp. $\mathcal{D}(\Gamma\mathbb{S})$) is canonically isomorphic to $\operatorname{FStab}\mathcal{D}(Q)$ (resp. the principal component $\operatorname{FStab}^\circ\mathcal{D}(\Gamma Q)$) of the space of $F$-stable stability conditions of $\mathcal{D}(Q)$ (resp. $\mathcal{D}(\Gamma Q)$). There are two applications. One is for the space $\operatorname{NStab}\mathcal{D}(\Gamma Q)$ of numerical stability conditions in $\operatorname{Stab}^\circ\mathcal{D}(\Gamma Q)$. We show that $\operatorname{NStab}\mathcal{D}(\Gamma Q)$ consists of $\operatorname{Br} Q/\operatorname{Br} \mathbb{S}$ many connected components, each of which is isomorphic to $\operatorname{Stab}^\circ\mathcal{D}(\Gamma\mathbb{S})$, for $(Q,\mathbb{S})$ is of type $(A_3, B_2)$ or $(D_4, G_2)$. The other is that we relate the $F$-stable stability conditions to the Gepner type stability conditions.Comment: Update versio

Contractible stability spaces and faithful braid group actions

We prove that any `finite-type' component of a stability space of a triangulated category is contractible. The motivating example of such a component is the stability space of the Calabi--Yau-$N$ category $\mathcal{D}(\Gamma_N Q)$ associated to an ADE Dynkin quiver. In addition to showing that this is contractible we prove that the braid group $\operatorname{Br}(Q)$ acts freely upon it by spherical twists, in particular that the spherical twist group $\operatorname{Br}(\Gamma_N Q)$ is isomorphic to $\operatorname{Br}(Q)$. This generalises Brav-Thomas' result for the $N=2$ case. Other classes of triangulated categories with finite-type components in their stability spaces include locally-finite triangulated categories with finite rank Grothendieck group and discrete derived categories of finite global dimension.Comment: Final version, to appear in Geom. Topo