arXiv subjects

Ulrike Riess

Publications and source records attributed to Ulrike Riess.

5 recordsLinked to original sources

arXiv2022

Wall divisors on irreducible symplectic orbifolds of Nikulin-type

We determine the wall divisors on irreducible symplectic orbifolds which are deformation equivalent to a special type of examples, called Nikulin orbifolds. The Nikulin orbifolds are obtained as partial resolutions in codimension 2 of a quotient by a symplectic involution of a Hilbert scheme of 2 points on a K3 surface. This builds on the previous article arXiv:2009.04873 in which the theory of wall divisors was generalized to orbifold singularities.

math.AG↗

arXiv2019

On the non-divisorial base locus of big and nef line bundles of K3^{[2]}-type varieties

We approach non-divisorial base loci of big and nef line bundles on irreducible symplectic varieties. While for K3 surfaces, only divisorial base loci can occur, nothing was known about the behaviour of non-divisorial base loci for more general irreducible symplectic varieties. We determine the base loci of all big and nef line bundles on the Hilbert scheme of two points on very general K3 surfaces of genus two and on their birational models. Remarkably, we find an ample line bundle with a non-trivial base locus in codimension two. We deduce that, generically in the moduli spaces of polarized K3$^{[2]}$-type varieties, the polarization is base point free.

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arXiv2018

Base divisors of big and nef line bundles on irreducible symplectic varieties

Under some conditions on the deformation type, which we expect to be satisfied for arbitrary irreducible symplectic varieties, we describe which big and nef line bundles on irreducible symplectic varieties have base divisors. In particular, we show that such base divisors are always irreducible and reduced. This is applied to understand the behaviour of divisorial base components of big and nef line bundles under deformations and for K3$^{[n]}$-type and Kum$^n$-type.

math.AG↗

arXiv2014

On the Beauville conjecture

We investigate Beauville's conjecture on the Chow ring of irreducible symplectic varieties. For special irreducible symplectic varieties we relate it to a conjecture on the existence of rational Lagrangian fibrations, which proves Beauville's conjecture in many new cases. We further apply the same techniques to reduce Beauville's conjecture to Picard rank two.

math.AG↗

arXiv2014

On the Chow ring of birational irreducible symplectic varieties

We show that the graded Chow rings of two birational irreducible symplectic varieties are isomorphic. This lifts a result known for the cohomology algebras to the level of Chow rings, despite the non-injectivity the cycle class map. In the special case of general Mukai flops, we present an alternative approach based on explicit calculations.

math.AG↗