Toric sheaves,stability and fibrations

For an equivariant reflexive sheaf over a polarised toric variety, we study slope stability of its reflexive pullback along a toric fibration. Examples of such fibrations include equivariant blow-ups and toric locally trivial fibrations. We show that stability (resp. unstability) is preserved under such pullbacks for so-called adiabatic polarisations. In the strictly semistable situation, under locally freeness assumptions, we provide a necessary and sufficient condition on the graded object to ensure stability of the pulled back sheaf. As applications, we provide various stable perturbations of semistable tangent sheaves, either by changing the polarisation, or by blowing-up a subvariety. Finally, our results apply uniformly in specific flat families and induce injective maps between the associated moduli spaces.     

Lazarsfeld-Mukai reflexive sheaves and their stability

Consider an ample and globally generated line bundle L on a smooth projective variety X of dimension N≥2 over ?. Let D be a smooth divisor in the complete linear system of L. We construct reflexive sheaves on X by an elementary transformation of a trivial bundle on X along certain globally generated torsion-free sheaves on D. The dual reflexive sheaves are called the Lazarsfeld-Mukai reflexive sheaves. We prove the μ_L-(semi)stability of such reflexive sheaves under certain conditions.     

Hyperholomorphic connections on coherent sheaves and stability

Let M be a hyperkähler manifold, and F a reflexive sheaf on M. Assume that F (away from its singularities) admits a connection ? with a curvature Θ which is invariant under the standard SU(2)-action on 2-forms. If Θ is square-integrable, such sheaf is called hyperholomorphic. Hyperholomorphic sheaves were studied at great length in [21]. Such sheaves are stable and their singular sets are hyperkähler subvarieties in M. In the present paper, we study sheaves admitting a connection with SU(2)-invariant curvature which is not necessary L ²-integrable. We show that such sheaves are polystable.     

Strong openness of multiplier ideal sheaves and optimal L~2 extension

In this paper, we reveal that our solution of Demailly's strong openness conjecture implies a matrix version of the conjecture; our solutions of two conjectures of Demailly-Koll′ar and Jonsson-Mustat?a implies the truth of twisted versions of the strong openness conjecture; our optimal L~2 extension implies Berndtsson's positivity of vector bundles associated to holomorphic fibrations over a unit disc.     

Tensor product varieties,perverse sheaves,and stability conditions

The space spanned by the class of simple perverse sheaves in Zheng (2008) without localization is isomorphic to the tensor product of a Verma module with a tensor product of irreducible integrable highest weight modules of the quantum enveloping algebra associated with a graph. Under the isomorphism, the simple perverse sheaves get identified with the canonical basis elements of the tensor product module. The two stability conditions coincide with the localization process in Zheng (2008), by using supports and singular supports of complexes of sheaves, respectively.     

Cat-valued sheaves

Let \(\mathcal{\widetilde{O}}\)(B) be the category of (open) subcategories of a topological groupoid B: In this paper we study Cat-valued sheaves over category \(\mathcal{\widetilde{O}}\)(B): The paper introduces a notion of categorical union, such that the categorical union of subcategories is a subcategory. We use this definition of categorical unions to define a categorical cover of a topological category. Instead of assuming a Grothendieck topology, we define Cat-valued sheaves in terms of the categorical cover defined in this paper. The main result is the following. For a fixed category C, the categories of local functorial sections from B to C define a Catvalued sheaf on \(\mathcal{\widetilde{O}}\)(B): Replacing C with a categorical group G; we find a CatGrp-valued sheaf on \(\mathcal{\widetilde{O}}\)(B): We also relate and distinguish our construction with the notion of stacks.     

Quantales and their sheaves

A quantale is a complete lattice provided with a binary multiplication which, in particular, distributes over in each variable. First we study the quantales, their morphisms, their points and the relations with the theory of locales: the case where the multiplication is just the meet. We describe the presheaves and sheaves on a quantale and exhibit a link between the corresponding toposes and quantum logic.Research supported by NATO grant 476/84.     

Relatively Noetherian rings, localization and sheaves. II: Structure sheaves

In the first part of this note, we have introduced a version of the (strong) second layer condition for ringsR which are relatively Noetherian with respect to some radical inR-mod and studied its impact on classical and symmetric localization theory. As an application, we now show how the relative version of the strong second layer condition allows us to endowK(), the generically closed subset of Spec(R) canonically associated to , with structure sheaves, which generalize most previously studied sheaf constructions in noncommutative algebra.     

Toric co-Higgs sheaves

We characterise and investigate co-Higgs sheaves and associated algebraic and combinatorial invariants on toric varieties. In particular, we compute explicit examples.     

Gorenstein injective sheaves

We define Gorenstein injective quasi-coherent sheaves, and prove that the notion is local in case the scheme is Gorenstein. We also give a new characterization of a Gorenstein scheme in terms of the total acyclicity of every acyclic complex of injective quasi-coherent modules.