arXiv subjects

Andrei Caldararu

Publications and source records attributed to Andrei Caldararu.

24 records · Page 2Linked to original sources

arXiv2005

Derived categories of sheaves: a skimming

These lecture notes were prepared for the workshop ``Algebraic Geometry: Presentations by Young Researchers'' in Snowbird, Utah, July 2004, and for the autumn school in Lukecin, Poland, September 2004. In six lectures I attempted to present a non-technical introduction to derived categories of sheaves on varieties, including some important results like: -- the description of the derived category of P^n; -- Serre duality; -- the Bondal-Orlov result about derived categories of varieties with ample or antiample canonical class; -- the Mukai-Bondal-Orlov-Bridgeland criterion for equivalence; -- equivalences for K3 surfaces and abelian varieties; -- invariance of Hochschild homology and cohomology under derived equivalence.

math.AG↗

arXiv2004

The Mukai pairing, II: the Hochschild-Kostant-Rosenberg isomorphism

We continue the study of the Hochschild structure of a smooth space that we began in our previous paper, examining implications of the Hochschild-Kostant-Rosenberg theorem. The main contributions of the present paper are: -- we introduce a generalization of the usual Mukai pairing on differential forms that applies to arbitrary manifolds; -- we give a proof of the fact that the natural Chern character map $K_0(X) \to HH_0(X)$ becomes, after the HKR isomorphism, the usual one $K_0(X) \to \bigoplus H^i(X, Ω_X^i)$; and -- we present a conjecture that relates the Hochschild and harmonic structures of a smooth space.

math.AG↗

arXiv2003

The Mukai pairing, I: the Hochschild structure

We study the Hochschild structure of a smooth space or orbifold, emphasizing the importance of a pairing defined on Hochschild homology which generalizes a similar pairing introduced by Mukai on the cohomology of a K3 surface. We discuss those properties of the structure which can be derived without appealing to the Hochschild-Kostant-Rosenberg isomorphism and Kontsevich formality, namely: -- functoriality of homology, commutation of push-forward with the Chern character, and adjointness with respect to the generalized pairing; -- formal Hirzebruch-Riemann-Roch and the Cardy condition from physics; -- invariance of the full Hochschild structure under Fourier-Mukai transforms. Connections with homotopy theory and TQFT's are discussed in an appendix. A separate paper treats consequences of the HKR isomorphism. Applications of these results to the study of a mirror symmetric analogue of Chen-Ruan's orbifold product will be presented in a future paper.

math.AG↗

arXiv2003

Algebraic deformations arising from orbifolds with discrete torsion

We develop methods for computing Hochschild cohomology groups and deformations of crossed product rings. We use these methods to find deformations of a ring associated to a particular orbifold with discrete torsion, and give a presentation of the center of the resulting deformed ring. This connects with earlier calculations by Vafa and Witten of chiral numbers and deformations of a similar orbifold.

math.KT↗

arXiv2001

Non-Fine Moduli Spaces of Sheaves on K3 Surfaces

In general, if M is a moduli space of stable sheaves on X, there is a unique alpha in the Brauer group of M such that a pi_M^* alpha^{-1}-twisted universal sheaf exists on X times M. In this paper we study the situation when X and M are K3 surfaces, and we identify alpha in terms of Mukai's map between the cohomology of X and of M (defined by means of a quasi-universal sheaf). We prove that the derived category of sheaves on X and the derived category of alpha-twisted sheaves on M are equivalent. This suggests a conjecture which describes, in terms of Hodge isometries of lattices, when derived categories of twisted sheaves on two K3 surfaces are equivalent. If proven true, this conjecture would generalize a theorem of Orlov and a recent result of Donagi-Pantev.

math.AG↗

arXiv2001

Derived Categories of Twisted Sheaves on Elliptic Threefolds

We construct an equivalence between the derived category of sheaves on an elliptic threefold without a section and a derived category of twisted sheaves (modules over an Azumaya algebra) on any small resolution of its relative Jacobian.

math.AG↗