Damien Calaque

Hochschild cohomology and Atiyah classes

Abstract In this paper we prove that on a smooth algebraic variety the HKR-morphism twisted by the square root of the Todd genus gives an isomorphism between the sheaf of poly-vector fields and the sheaf of poly-differential operators, both considered as derived Gerstenhaber algebras. In particular we obtain an isomorphism between Hochschild cohomology and the cohomology of poly-vector fields which is compatible with the Lie bracket and the cupproduct. The latter compatibility is an unpublished result by Kontsevich. Our proof is set in the framework of Lie algebroids and so applies without modification in much more general settings as well.

Universal KZB Equations: The Elliptic Case

We define a universal version of the Knizhnik–Zamolodchikov–Bernard (KZB) connection in genus 1. This is a flat connection over a principal bundle on the moduli space of elliptic curves with marked points. It restricts to a flat connection on configuration spaces of points on elliptic curves, which can be used for proving the formality of the pure braid groups on genus 1 surfaces. We study the monodromy of this connection and show that it gives rise to a relation between the KZ associator and a generating series for iterated integrals of Eisenstein forms. We show that the universal KZB connection is realized as the usual KZB connection for simple Lie algebras, and that in the \(\mathfrak {sl}_n\) case this realization factors through the Cherednik algebras. This leads us to define a functor from the category of equivariant D-modules on \(\mathfrak {sl}_n\) to that of modules over the Cherednik algebra, and to compute the character of irreducible equivariant D-modules over \(\mathfrak {sl}_n\) that are supported on the nilpotent cone.

Two interacting Hopf algebras of trees: A Hopf-algebraic approach to composition and substitution of B-series

Hopf algebra structures on rooted trees are by now a well-studied object, especially in the context of combinatorics. In this work we consider a Hopf algebra H by introducing a coproduct on a (commutative) algebra of rooted forests, considering each tree of the forest (which must contain at least one edge) as a Feynman-like graph without loops. The primitive part of the graded dual is endowed with a pre-Lie product defined in terms of insertion of a tree inside another. We establish a surprising link between the Hopf algebra H obtained this way and the well-known Connes-Kreimer Hopf algebra of rooted trees by means of a natural H-bicomodule structure on the latter. This enables us to recover recent results in the field of numerical methods for differential equations due to Chartier, Hairer and Vilmart as well as Murua.

Shifted Poisson structures and deformation quantization

This paper is a sequel to [PTVV]. We develop a general and flexible context for differential calculus in derived geometry, including the de Rham algebra and poly-vector fields. We then introduce the formalism of formal derived stacks and prove formal localization and gluing results. These allow us to define shifted Poisson structures on general derived Artin stacks, and prove that the non-degenerate Poisson structures correspond exactly to shifted symplectic forms. Shifted deformation quantization for a derived Artin stack endowed with a shifted Poisson structure is discussed in the last section. This paves the way for shifted deformation quantization of many interesting derived moduli spaces, like those studied in [PTVV] and probably many others.

Lectures on Duflo Isomorphisms in Lie Algebra and Complex Geometry

Duflo isomorphism first appeared in Lie theory and representation theory. It is an isomorphism between invariant polynomials of a Lie algebra and the center of its universal enveloping algebra, generalizing the pioneering work of Harish-Chandra on semi-simple Lie algebras. Later on, Duflo’s result was refound by Kontsevich in the framework of deformation quantization, who also observed that there is a similar isomorphism between Dolbeault cohomology of holomorphic polyvector fields on a complex manifold and its Hochschild cohomology. The present book, which arose from a series of lectures by the first author at ETH, derives these two isomorphisms from a Duflo-type result for Q-manifolds. All notions mentioned above are introduced and explained in the book, the only prerequisites being basic linear algebra and differential geometry. In addition to standard notions such as Lie (super)algebras, complex manifolds, Hochschild and Chevalley–Eilenberg cohomologies, spectral sequences, Atiyah and Todd classes, the graphical calculus introduced by Kontsevich in his seminal work on deformation quantization is addressed in details. The book is well-suited for graduate students in mathematics and mathematical physics as well as for researchers working in Lie theory, algebraic geometry and deformation theory.

Lagrangian structures on mapping stacks and semi-classical TFTs

We extend a recent result of Pantev-Toen-Vaquie-Vezzosi, who constructed shifted symplectic structures on derived mapping stacks having a Calabi-Yau source and a shifted symplectic target. Their construction gives a clear conceptual framework for the so-called AKSZ formalism. We extend the PTVV construction to derived mapping stacks with boundary conditions, which is required in most applications to quantum field theories (see e.g. the work of Cattaneo-Felder on the Poisson sigma model, and the recent work of Cattaneo-Mnev-Reshetikhin). We provide many examples of Lagrangian and symplectic structures that can be recovered in this way. We finally give an application to topological field theories (TFTs). We expect that our approach will help to rigorously constuct a 2 dimensional TFT introduced by Moore and Tachikawa. A subsequent paper will be devoted to the construction of fully extended TFTs (in the sense of Baez-Dolan and Lurie) from mapping stacks.We give a new way to produce examples of Lagrangians in shifted symplectic derived stacks, based on multiple intersections. Specifically, we show that an m-fold homotopy fiber product of Lagrangians in a shifted symplectic derived stack its itself Lagrangian in a certain cyclic product of pairwise homotopy fiber products of the Lagrangians.

Lectures on tensor categories

We give a review of some recent developments in the theory of tensor categories. The topics include realizability of fusion rings, Ocneanu rigidity, module categories, weak Hopf algebras, Morita theory for tensor categories, lifting theory, categorical dimensions, Frobenius- Perron dimensions, classification of tensor categories.Here is an introduction to the theory of quantum groups with emphasis on the spectacular connections with knot theory and Drinfelds recent fundamental contributions. It presents the quantum groups attached to SL2 as well as the basic concepts of the theory of Hopf algebras. Coverage also focuses on Hopf algebras that produce solutions of the Yang-Baxter equation and provides an account of Drinfelds elegant treatment of the monodromy of the Knizhnik-Zamolodchikov equations.

Formality theorems for Hochschild chains in the Lie algebroid setting

Abstract In this paper we prove Lie algebroid versions of Tsygans formality conjecture for Hochschild chains both in the smooth and holomorphic settings. Our result in the holomorphic setting implies a version of Tsygans formality conjecture for Hochschild chains of the structure sheaf of any complex manifold. The proofs are based on the use of Kontsevichs quasi-isomorphism for Hochschild cochains of ℝ[[y 1, …, yd ]], Shoikhets quasi-isomorphism for Hochschild chains of ℝ[[y 1, …, yd ]], and Fedosovs resolutions of the natural analogues of Hochschild (co)chain complexes associated with a Lie algebroid. In the smooth setting we discuss an application of our result to the description of quantum traces for a Poisson Lie algebroid.

Formality for lie algebroids

Using Dolgushev’s generalization of Fedosov’s method for deformation quantization, we give a positive answer to a question of P. Xu: can one prove a formality theorem for Lie algebroids ? As a direct application of this result, we obtain that any triangular Lie bialgebroid is quantizable.

Weak quantization of Poisson structures

Abstract In this paper we prove that any Poisson structure on a sheaf of Lie algebroids admits a weak deformation quantization, and give a sufficient condition for such a Poisson structure to admit an actual deformation quantization. We also answer the corresponding classification problems. In the complex symplectic case, we recover in particular some results of Nest-Tsygan and Polesello-Schapira. We begin the paper with a recollection of known facts about deformation theory of cosimplicial differential graded Lie algebras.