Abstract

This paper is intended both as an introduction to the algebraic geometry of holomorphic Poisson brackets, and as a survey of results on the classification of projective Poisson manifolds that have been obtained in the past 20 years. It is based on the lecture series delivered by the author at the Poisson 2016 Summer School in Geneva. The paper begins with a detailed treatment of Poisson surfaces, including adjunction, ruled surfaces and blowups, and leading to a statement of the full birational classification. We then describe several constructions of Poisson threefolds, outlining the classification in the regular case, and the case of rank-one Fano threefolds (such as projective space). Following a brief introduction to the notion of Poisson subspaces, we discuss Bondal’s conjecture on the dimensions of degeneracy loci on Poisson Fano manifolds. We close with a discussion of log symplectic manifolds with simple normal crossings degeneracy divisor, including a new proof of the classification in the case of rank-one Fano manifolds.

Highlights

  • This paper is an introduction to the geometry of holomorphic Poisson structures, i.e. Poisson brackets on the ring of holomorphic or algebraic functions on a complex manifold or algebraic variety

  • This paper serves a second purpose: it is an overview of results on the classification of projective Poisson manifolds that have been obtained by several authors over the past couple of decades, with some added context for the results and the occasional new proof

  • We will focus on the related problems of construction and classification: how do we produce holomorphic Poisson structures on compact complex manifolds, and how do we know when we have found them all?

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Summary

Basic definitions and aims

This paper is an introduction to the geometry of holomorphic Poisson structures, i.e. Poisson brackets on the ring of holomorphic or algebraic functions on a complex manifold or algebraic variety (and sometimes on more singular objects, such as schemes and analytic spaces). It grew out of a mini-course delivered by the author at the “Poisson 2016” summer school in Geneva. The first (albeit minor) difference comes already in the definition: while a Poisson bracket on a C∞ manifold is defined by a Poisson bracket on the ring of global smooth functions, this definition is no longer appropriate in the holomorphic setting.

Jacobi identity:
What is meant by classification?
The role of Fano manifolds
Basics of Poisson surfaces
Local structure
Poisson structures on the projective plane
Anticanonical divisors and adjunction
Anticanonical divisors
Adjunction on Poisson surfaces
Poisson structures on ruled surfaces
Compactified cotangent bundles
Relationship with co-Higgs fields
Classification of ruled Poisson surfaces
Blowups and minimal surfaces
Blowing up surfaces
Blowing up Poisson brackets
Birational classification of Poisson surfaces
Symplectic surfaces
Surfaces with degenerate Poisson structures
Poisson threefolds
Regular Poisson structures
Poisson structures from pencils of surfaces
Jacobian Poisson structures on C3
Pencils of symplectic leaves
Poisson structures from pencils on P3
Further constructions
Poisson structures on P3 and other Fano threefolds
Poisson subspaces and degeneracy loci
Poisson subspaces and multiderivations
Vector fields and multiderivations
Log symplectic structures
Definition and examples
Some classification results
Topological constraints from residue theory
Intersection of components and biresidues

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