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Lagrangian 4-planes in holomorphic symplectic varieties of K3[4]-type

Benjamin Bakker, Andrei Jorza (2014)

Open Mathematics

We classify the cohomology classes of Lagrangian 4-planes ℙ4 in a smooth manifold X deformation equivalent to a Hilbert scheme of four points on a K3 surface, up to the monodromy action. Classically, the Mori cone of effective curves on a K3 surface S is generated by nonnegative classes C, for which (C, C) ≥ 0, and nodal classes C, for which (C, C) = −2; Hassett and Tschinkel conjecture that the Mori cone of a holomorphic symplectic variety X is similarly controlled by “nodal” classes C such that...

Local-global divisibility of rational points in some commutative algebraic groups

Roberto Dvornicich, Umberto Zannier (2001)

Bulletin de la Société Mathématique de France

Let 𝒜 be a commutative algebraic group defined over a number field  k . We consider the following question:Let r be a positive integer and let P 𝒜 ( k ) . Suppose that for all but a finite number of primes v of k , we have P = r D v for some D v 𝒜 ( k v ) . Can one conclude that there exists D 𝒜 ( k ) such that P = r D ?A complete answer for the case of the multiplicative group 𝔾 m is classical. We study other instances and in particular obtain an affirmative answer when r is a prime and  𝒜 is either an elliptic curve or a torus of small dimension...

Local-global principle for certain biquadratic normic bundles

Yang Cao, Yongqi Liang (2014)

Acta Arithmetica

Let X be a proper smooth variety having an affine open subset defined by the normic equation N k ( a , b ) / k ( x ) = Q ( t , . . . , t ) ² over a number field k. We prove that: (1) the failure of the local-global principle for zero-cycles is controlled by the Brauer group of X; (2) the analogue for rational points is also valid assuming Schinzel’s hypothesis.

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