Cambrian lattices are fractionally Calabi-Yau via 2-cluster combinatorics

TL;DR

This paper proves that Cambrian lattices associated with finite Coxeter diagrams are fractionally Calabi-Yau, extending previous results and connecting lattice combinatorics with 2-cluster tilting theory.

Contribution

It establishes the fractional Calabi-Yau property for Cambrian lattices of all finite types, confirming a conjecture and linking lattice intervals to 2-cluster tilting objects.

Findings

Cambrian lattices are fractionally Calabi-Yau for any finite Coxeter diagram.

For crystallographic diagrams, Cambrian lattices correspond to torsion class lattices of hereditary algebras.

The paper computes the Calabi-Yau dimension of Cambrian lattices using combinatorics of specific intervals.

Abstract

Reading constructed a Cambrian lattice $C_\Gamma$ for each oriented finite type Coxeter diagram $\Gamma$. We show that the derived category of representations of $C_\Gamma$ is fractionally Calabi-Yau for any $\Gamma$, confirming a conjecture of Chapoton. This extends a result of Rognerud for Cambrian lattices of type $A$ with linear orientation, better known as Tamari lattices. If $\Gamma$ is crystallographic, then $C_\Gamma$ is given by the lattice of torsion classes of any hereditary algebra $\Lambda$ of type $\Gamma$. In this case we introduce and study a class of intervals in $C_\Gamma$ whose combinatorics matches the combinatorics of $2$-cluster tilting objects in the 2-cluster category of $\Lambda$. This allows us to compute the Calabi-Yau dimension of $C_\Gamma$.