## Generic bases for cluster algebras and the Chamber Ansatz

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- by Christof Geiß, Bernard Leclerc and Jan Schröer PDF
- J. Amer. Math. Soc.
**25**(2012), 21-76 Request permission

## Abstract:

Let $Q$ be a finite quiver without oriented cycles, and let $\Lambda$ be the corresponding preprojective algebra. Let $\mathfrak {g}$ be the Kac-Moody Lie algebra with Cartan datum given by $Q$, and let $W$ be its Weyl group. With $w \in W$, there is associated a unipotent cell $N^w$ of the Kac-Moody group with Lie algebra $\mathfrak {g}$. In previous work we proved that the coordinate ring $\mathbb {C}[N^w]$ of $N^w$ is a cluster algebra in a natural way. A central role is played by generating functions $\varphi _X$ of Euler characteristics of certain varieties of partial composition series of $X$, where $X$ runs through all modules in a Frobenius subcategory $\mathcal {C}_w$ of the category of nilpotent $\Lambda$-modules. The first aim of this article is to compare the function $\varphi _X$ with the so-called cluster character of $X$, which is defined in terms of the Euler characteristics of quiver Grassmannians. We show that for every $X$ in $\mathcal {C}_w$, $\varphi _X$ coincides, after an appropriate change of variables, with the cluster character of Fu and Keller associated with $X$ using any cluster-tilting object $T$ of $\mathcal {C}_w$. A crucial ingredient of the proof is the construction of an isomorphism between varieties of partial composition series of $X$ and certain quiver Grassmannians. This isomorphism is obtained in a very general setup and should be of interest in itself. Another important tool of the proof is a representation-theoretic version of the Chamber Ansatz of Berenstein, Fomin and Zelevinsky, adapted to Kac-Moody groups. As an application, we get a new description of a generic basis of the cluster algebra $\mathcal {A}(\underline {\Gamma }_T)$ obtained from $\mathcal {C}[N^w]$ via specialization of coefficients to 1. Here*generic*refers to the representation varieties of a quiver potential arising from the cluster-tilting module $T$. For the special case of coefficient-free acyclic cluster algebras this proves a conjecture by Dupont.

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## Additional Information

**Christof Geiß**- Affiliation: Instituto de Matemáticas, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 México D.F., México
- MR Author ID: 326818
- Email: christof@math.unam.mx
**Bernard Leclerc**- Affiliation: LMNO, Université de Caen, CNRS, UMR 6139, F-14032 Caen Cedex, France
- MR Author ID: 327337
- Email: leclerc@math.unicaen.fr
**Jan Schröer**- Affiliation: Mathematisches Institut, Universität Bonn, Endenicher Allee 60, 53115 Bonn, Germany
- MR Author ID: 633566
- Email: schroer@math.uni-bonn.de
- Received by editor(s): May 13, 2010
- Received by editor(s) in revised form: May 13, 2011
- Published electronically: August 10, 2011
- © Copyright 2011
American Mathematical Society

The copyright for this article reverts to public domain 28 years after publication. - Journal: J. Amer. Math. Soc.
**25**(2012), 21-76 - MSC (2010): Primary 13F60, 14M15, 14M99, 16G20, 20G44
- DOI: https://doi.org/10.1090/S0894-0347-2011-00715-7
- MathSciNet review: 2833478