arXiv subjects

Lukas Bertsch

Publications and source records attributed to Lukas Bertsch.

4 recordsLinked to original sources

arXiv2025

Stacky Resolutions of Kleinian Singularities and Nakajima Quiver Varieties

We construct a class of noncommutative crepant resolutions of any Kleinian singularity as noncommutative sheaves of algebras over its crepant partial resolutions. We argue that such resolutions are Morita equivalent to the canonical orbifold resolutions of the partial resolutions. Further, we study Hilbert schemes of points on both the crepant partial and noncommutative resolutions and show that they are Nakajima quiver varieties. Finally, we describe the nef and movable cones of these Hilbert schemes of points using tautological bundles on the crepant partial resolutions.

math.AG↗

arXiv2025

Quiver Schemes for Nongeneric Stability and Cornering

We use the Le Bruyn--Procesi theorem to prove several results on quiver schemes for nongeneric stability conditions: We show that the stability-zero finite-type Nakajima quiver schemes are reduced points and give an example of a closely related nonreduced quiver scheme. In broader generality, we prove that adding modules supported on stability-zero vertices induces closed embeddings of quiver schemes, and show how in many cases the quiver scheme associated with the cornered algebra defines a limit to this system of embeddings. As an application, we show that there is an isomorphism between the underlying reduced schemes of certain equivariant Quot schemes and Nakajima quiver varieties.

math.AG↗

arXiv2024

Kleinian singularities: some geometry, combinatorics and representation theory

We review the relationship between discrete groups of symmetries of Euclidean three-space, constructions in algebraic geometry around Kleinian singularities including versions of Hilbert and Quot schemes, and their relationship to finite-dimensional and affine Lie algebras via the McKay correspondence. We focus on combinatorial aspects, such as the enumeration of certain types of partition-like objects, reviewing in particular a recently developed root-of-unity-substitution calculus. While the most complete results are in type A, we also develop aspects of the theory in type D, and end with some questions about the exceptional type E cases.

math.AG↗

arXiv2023

Euler characteristics of affine ADE Nakajima quiver varieties via collapsing fibers

We prove a universal substitution formula that compares generating series of Euler characteristics of Nakajima quiver varieties associated with affine ADE diagrams at generic and at certain nongeneric stability conditions via a study of collapsing fibres in the associated variation of GIT map, unifying and generalising earlier results of the last two authors with N\'emethi and of Nakajima. As a special case, we compute generating series of Euler characteristics of noncommutative Quot schemes of Kleinian orbifolds. In type A and rank 1, we give a second, combinatorial proof of our substitution formula, using torus localisation and partition enumeration. This gives a combinatorial model of the fibers of the variation of GIT map, and also leads to relations between our results and the representation theory of the affine and finite Lie algebras in type A.

math.AG↗