4 citations · 4 across the 3 of their papers we have counts for
10 papers · 1 filter
Kummer surfaces for the selfproduct of the cuspidal rational curve
Stefan Schroeer
The classical Kummer construction attaches to an abelian surface a K3 surface. As Shioda and Katsura showed, this construction breaks down for supersingular abelian surfaces in cha…
The Brauer group of analytic K3 surfaces
Daniel Huybrechts, Stefan Schroeer
We show that for complex analytic K3 surfaces any torsion class in H^2(X,O_X^*) comes from an Azumaya algebra. In other words, the Brauer group equals the cohomological Brauer grou…
Curves with only triple ramification
Stefan Schroeer
I show that the set of smooth curves of genus g admitting branched coverings X->P^1 with only triple ramification points has dimension at least max(2g-3,g). In characteristic two,…
The strong Franchetta Conjecture in arbitrary characteristics
Stefan Schroeer
Using Moriwaki's calculation of the Q-Picard group for the moduli space of curves, I prove the strong Franchetta Conjecture in all characteristics. That is, the canonical class gen…
Existence of vector bundles and global resolutions for singular surfaces
Stefan Schroeer, Gabriele Vezzosi
We prove two results about vector bundles on singular algebraic surfaces. First, on proper surfaces there are vector bundles of rank two with arbitrarily large second Chern number…
Hilbert's Theorem 90 and algebraic spaces
Stefan Schroeer
In modern form, Hilbert's Theorem 90 tells us that R^1f_*(G_m)=0, where f is the canonical map between the etale site and the Zariski site of a scheme X. I construct examples showi…