2,064 research outputs found
Abelian surfaces with odd bilevel structure
The moduli space of abelian surfaces with polarisation of type (1,t) and a
bilevel structure is of general type if t is odd and at least 17.Comment: 21 page
Fundamental groups of toroidal compactifications
We compute the fundamental group of a toroidal compactification of a
Hermitian locally symmetric space , without assuming either that
is neat or that it is arithmetic. We also give bounds for the first
Betti number.Comment: Final version. Fixes error pointed out by M. Roessler, leading to
slightly but significantly changed statements: improved notatio
Abelianisation of orthogonal groups and the fundamental group of modular varieties
We study the commutator subgroup of integral orthogonal groups belonging to
indefinite quadratic forms. We show that the index of this commutator is 2 for
many groups that occur in the construction of moduli spaces in algebraic
geometry, in particular the moduli of K3 surfaces. We give applications to
modular forms and to computing the fundamental groups of some moduli spaces
Heisenberg-invariant Kummer surfaces
We study the geometry of Nieto's quintic threefold (Barth & Nieto, J. Alg.
Geom. 3, 1994) and the Kummer and abelian surfaces that correspond to special
loci.Comment: Plain TeX, 17 pages. Final version, with minor corrections, to appear
in Proc. Edinburgh Math. So
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