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Symplectic involutions on deformations of K3[2]

Giovanni Mongardi (2012)

Open Mathematics

Let X be a hyperkähler manifold deformation equivalent to the Hilbert square of a K3 surface and let φ be an involution preserving the symplectic form. We prove that the fixed locus of φ consists of 28 isolated points and one K3 surface, and moreover that the anti-invariant lattice of the induced involution on H 2(X, ℤ) is isomorphic to E 8(−2). Finally we show that any couple consisting of one such manifold and a symplectic involution on it can be deformed into a couple consisting of the Hilbert...

Symplectic structures on moduli spaces of framed sheaves on surfaces

Francesco Sala (2012)

Open Mathematics

We provide generalizations of the notions of Atiyah class and Kodaira-Spencer map to the case of framed sheaves. Moreover, we construct closed two-forms on the moduli spaces of framed sheaves on surfaces. As an application, we define a symplectic structure on the moduli spaces of framed sheaves on some birationally ruled surfaces.

Tensor product theorem for Hitchin pairs – An algebraic approach

V. Balaji, A.J. Parameswaran (2011)

Annales de l’institut Fourier

We give an algebraic approach to the study of Hitchin pairs and prove the tensor product theorem for Higgs semistable Hitchin pairs over smooth projective curves defined over algebraically closed fields of characteristic zero and characteristic p , with p satisfying some natural bounds. We also prove the corresponding theorem for polystable Hitchin pairs.

The additive group actions on -homology planes

Kayo Masuda, Masayoshi Miyanishi (2003)

Annales de l’institut Fourier

In this article, we prove that a -homology plane X with two algebraically independent G a -actions is isomorphic to either the affine plane or a quotient of an affine hypersurface x y = z m - 1 in the affine 3 -space via a free / m -action, where m is the order of a finite group H 1 ( X ; ) .

The arithmetic of certain del Pezzo surfaces and K3 surfaces

Dong Quan Ngoc Nguyen (2012)

Journal de Théorie des Nombres de Bordeaux

We construct del Pezzo surfaces of degree 4 violating the Hasse principle explained by the Brauer-Manin obstruction. Using these del Pezzo surfaces, we show that there are algebraic families of K 3 surfaces violating the Hasse principle explained by the Brauer-Manin obstruction. Various examples are given.

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