arXiv subjects

Christof Geiss

Publications and source records attributed to Christof Geiss.

21 records · Page 2Linked to original sources

arXiv2005

Cluster algebras of finite type and positive symmetrizable matrices

The paper is motivated by an analogy between cluster algebras and Kac-Moody algebras: both theories share the same classification of finite type objects by familiar Cartan-Killing types. However the underlying combinatorics beyond the two classifications is different: roughly speaking, Kac-Moody algebras are associated with (symmetrizable) Cartan matrices, while cluster algebras correspond to skew-symmetrizable matrices. We study an interplay between the two classes of matrices, in particular, establishing a new criterion for deciding whether a given skew-symmetrizable matrix gives rise to a cluster algebra of finite type.

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arXiv2005

Verma modules and preprojective algebras

We give a geometric construction of the Verma modules of a symmetric Kac-Moody Lie algebra in terms of constructible functions on the varieties of nilpotent finite-dimensional modules of the corresponding preprojective algebra.

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arXiv2005

Semicanonical bases and preprojective algebras

We study the multiplicative properties of the dual of Lusztig's semicanonical basis.The elements of this basis are naturally indexed by theirreducible components of Lusztig's nilpotent varieties, whichcan be interpreted as varieties of modules over preprojective algebras.We prove that the product of two dual semicanonical basis vectorsis again a dual semicanonical basis vector provided the closure ofthe direct sum of thecorresponding two irreducible components is again an irreducible component.It follows that the semicanonical basis and the canonical basiscoincide if and only if we are in Dynkin type $A_n$ with $n \leq 4$.Finally, we provide a detailed study of the varieties of modules over the preprojectivealgebra of type $A_5$.We show that in this case the multiplicative properties ofthe dual semicanonical basis are controlled by the Ringel form of a certain tubular algebra of type (6,3,2) and by thecorresponding elliptic root system of type $E_8^{(1,1)}$.

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