10 papers
Elliptic curves over the rational numbers with semi-abelian reduction and two-division points
Stefan Schröer
We classify elliptic curves over the rationals whose Néron model over the integers is semi-abelian, with good reduction at p=2, and whose Mordell--Weil group contains an element of…
Unirationality and geometric unirationality for hypersurfaces in positive characteristics
Keiji Oguiso, Stefan Schröer
Building on work of Segre and Koll'ar on cubic hypersurfaces, we construct over imperfect fields of characteristic p\geq 3 particular hypersurfaces of degree p, which show that geo…
Kummer surfaces associated with group schemes
Shigeyuki Kondo, Stefan Schröer
We introduce Kummer surfaces X=Km(CxC) with the group scheme G=mu_2 acting on the self-product of the rational cuspidal curve in characteristic two. The resulting quotients are nor…
On fibrations whose geometric fibers are nonreduced
Stefan Schroeer
We give a bound on embedding dimensions of geometric generic fibers in terms of the dimension of the base, for fibrations in positive characteristic. This generalizes the well-know…
The Hilbert scheme of points for supersingular abelian surfaces
Stefan Schroeer
We analyse the geometry of Hilbert schemes of points on abelian surfaces and Beauville's generalized Kummer varieties in positive characteristics. The main result is that, in chara…
The T^1-lifting theorem in positive characteristic
Stefan Schroeer
Replacing symmetric powers by divided powers and working over Witt vectors instead of ground fields, I generalize Kawamatas T^1-lifting theorem to characteristic p>0. Combined with…