Symplectic graphs and their automorphisms

Exotic iterated Dehn twists

Consider cotangent bundles of exotic spheres, with their canonical symplectic structure. They admit automorphisms which preserve the part at infinity of one fibre, and which are analogous to the square of a Dehn twist. Pursuing that analogy, we show that they have infinite order up to isotopy (inside the group of all automorphisms with the same behaviour).

The Dihedral Group D5 as Group of Symplectic Automorphisms on K3 Surfaces

We prove that if a K3 surface X admits Z/5Z as group of symplectic automorphisms, then it actually admits D5 as group of symplectic automorphisms. The orthogonal complement to the D5-invariants in the second cohomology group of X is a rank 16 lattice, L. It is known that L does not depend on X: we prove that it is isometric to a lattice recently described by R. L. Griess Jr. and C. H. Lam. We a...

Elliptic K3 Surfaces with Abelian and Dihedral Groups of Symplectic Automorphisms

We analyze K3 surfaces admitting an elliptic fibration E and a finite group G of symplectic automorphisms preserving this elliptic fibration. We construct the quotient elliptic fibration E/G comparing its properties to the ones of E. We show that if E admits an n-torsion section, its quotient by the group of automorphisms induced by this section admits again an n-torsion section. Considering au...

Some Remarks on Symplectic Automorphisms

The Dihedral Group D5 as a Group of Symplectic Automorphisms on K3 Surfaces

We prove that if a K3 surface X admits Z/5Z as a group of symplectic automorphisms, then it actually admits D5 as a group of symplectic automorphisms. The orthogonal complement to the D5-invariants in the second cohomology group of X is a rank 16 lattice, L. It is known that L does not depend on X: we prove that it is isometric to a lattice recently described by R. L. Griess Jr. and C. H. Lam. ...