Toric Topology

534 Pages·2015·3.54 MB·English

by  Victor M. Buchstaber, Taras E. Panov

Mathematical
Surveys
and
Monographs
Volume 204
Toric Topology
Victor M. Buchstaber
Taras E. Panov
American Mathematical Society
Toric Topology

Mathematical
Surveys
and
Monographs
Volume 204
Toric Topology
Victor M. Buchstaber
Taras E. Panov
American Mathematical Society
Providence, Rhode Island
EDITORIAL COMMITTEE
Robert Guralnick ConstantinTeleman
Michael A. Singer, Chair Michael I. Weinstein
Benjamin Sudakov
2010 Mathematics Subject Classification. Primary 13F55, 14M25,32Q55, 52B05, 53D12,
55N22, 55N91, 55Q15 57R85, 57R91.
For additional informationand updates on this book, visit
www.ams.org/bookpages/surv-204
Library of Congress Cataloging-in-Publication Data
Buchstaber,V.M.
Torictopology/VictorM.Buchstaber,TarasE.Panov.
pagescm. –(Mathematicalsurveysandmonographs;volume204)
Includesbibliographicalreferencesandindex.
ISBN978-1-4704-2214-1(alk.paper)
1. Toric varieties. 2. Algebraic varieties. 3. Algebraic topology. 4. Geometry, Algebraic.
I.Panov,TarasE.,1975– II.Title
QA613.2.B82 2015
516.3(cid:2)5–dc23 2015006771
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Contents
Introduction ix
Chapter guide x
Acknowledgements xiii
Chapter 1. Geometry and Combinatorics of Polytopes 1
1.1. Convex polytopes 1
1.2. Gale duality and Gale diagrams 9
1.3. Face vectors and Dehn–Sommerville relations 14
1.4. Characterising the face vectors of polytopes 19
Polytopes: Additional Topics 25
1.5. Nestohedra and graph-associahedra 25
1.6. Flagtopes and truncated cubes 38
1.7. Differential algebra of combinatorial polytopes 44
1.8. Families of polytopes and differential equations 48
Chapter 2. Combinatorial Structures 55
2.1. Polyhedral fans 56
2.2. Simplicial complexes 59
2.3. Barycentric subdivision and flag complexes 64
2.4. Alexander duality 66
2.5. Classes of triangulated spheres 69
2.6. Triangulated manifolds 75
2.7. Stellar subdivisions and bistellar moves 78
2.8. Simplicial posets and simplicial cell complexes 81
2.9. Cubical complexes 83
Chapter 3. Combinatorial Algebra of Face Rings 91
3.1. Face rings of simplicial complexes 92
3.2. Tor-algebras and Betti numbers 97
3.3. Cohen–Macaulay complexes 104
3.4. Gorenstein complexes and Dehn–Sommerville relations 111
3.5. Face rings of simplicial posets 114
Face Rings: Additional Topics 121
3.6. Cohen–Macaulay simplicial posets 121
3.7. Gorenstein simplicial posets 125
3.8. Generalised Dehn–Sommerville relations 127
Chapter 4. Moment-Angle Complexes 129
4.1. Basic definitions 131
4.2. Polyhedral products 135
v
vi CONTENTS
4.3. Homotopical properties 139
4.4. Cell decomposition 143
4.5. Cohomology ring 144
4.6. Bigraded Betti numbers 150
4.7. Coordinate subspace arrangements 157
Moment-Angle Complexes: Additional Topics 162
4.8. Free and almost free torus actions on moment-angle complexes 162
4.9. Massey products in the cohomology of moment-angle complexes 168
4.10. Moment-angle complexes from simplicial posets 171
Chapter 5. Toric Varieties and Manifolds 179
5.1. Classical construction from rational fans 179
5.2. Projective toric varieties and polytopes 183
5.3. Cohomology of toric manifolds 185
5.4. Algebraic quotient construction 188
5.5. Hamiltonian actions and symplectic reduction 195
Chapter 6. Geometric Structures on Moment-Angle Manifolds 201
6.1. Intersections of quadrics 201
6.2. Moment-angle manifolds from polytopes 205
6.3. Symplectic reduction and moment maps revisited 209
6.4. Complex structures on intersections of quadrics 212
6.5. Moment-angle manifolds from simplicial fans 215
6.6. Complex structures on moment-angle manifolds 219
6.7. Holomorphic principal bundles and Dolbeault cohomology 224
6.8. Hamiltonian-minimal Lagrangian submanifolds 231
Chapter 7. Half-Dimensional Torus Actions 239
7.1. Locally standard actions and manifolds with corners 240
7.2. Toric manifolds and their quotients 242
7.3. Quasitoric manifolds 243
7.4. Locally standard T-manifolds and torus manifolds 257
7.5. Topological toric manifolds 278
7.6. Relationship between different classes of T-manifolds 282
7.7. Bounded flag manifolds 284
7.8. Bott towers 287
7.9. Weight graphs 302
Chapter 8. Homotopy Theory of Polyhedral Products 313
8.1. Rational homotopy theory of polyhedral products 314
8.2. Wedges of spheres and connected sums of sphere products 321
8.3. Stable decompositions of polyhedral products 326
8.4. Loop spaces, Whitehead and Samelson products 331
8.5. The case of flag complexes 340
Chapter 9. Torus Actions and Complex Cobordism 347
9.1. Toric and quasitoric representatives in complex bordism classes 347
9.2. The universal toric genus 357
9.3. Equivariant genera, rigidity and fibre multiplicativity 364
9.4. Isolated fixed points: localisation formulae 367
CONTENTS vii
9.5. Quasitoric manifolds and genera 376
9.6. Genera for homogeneous spaces of compact Lie groups 380
9.7. Rigid genera and functional equations 385
Appendix A. Commutative and Homological Algebra 395
A.1. Algebras and modules 395
A.2. Homological theory of graded rings and modules 398
A.3. Regular sequences and Cohen–Macaulay algebras 405
A.4. Formality and Massey products 409
Appendix B. Algebraic Topology 413
B.1. Homotopy and homology 413
B.2. Elements of rational homotopy theory 424
B.3. Eilenberg–Moore spectral sequences 426
B.4. Group actions and equivariant topology 428
B.5. Stably complex structures 433
B.6. Weights and signs of torus actions 434
Appendix C. Categorical Constructions 439
C.1. Diagrams and model categories 439
C.2. Algebraic model categories 444
C.3. Homotopy limits and colimits 450
Appendix D. Bordism and Cobordism 453
D.1. Bordism of manifolds 453
D.2. Thom spaces and cobordism functors 454
D.3. Oriented and complex bordism 457
D.4. Characteristic classes and numbers 463
D.5. Structure results 467
D.6. Ring generators 468
Appendix E. Formal Group Laws and Hirzebruch Genera 473
E.1. Elements of the theory of formal group laws 473
E.2. Formal group law of geometric cobordisms 477
E.3. Hirzebruch genera (complex case) 479
E.4. Hirzebruch genera (oriented case) 486
E.5. Krichever genus 488
Bibliography 495
Index 511

Introduction
Traditionally, the study of torus actions on topological spaces has beenconsid-
eredasaclassicalfieldofalgebraictopology.Specificproblemsconnectedwithtorus
actionsariseindifferentareasofmathematicsandmathematicalphysics, whichre-
sults in permanent interest in the theory, new applications and penetration of new
ideas into topology.
Since the 1970s, algebraic and symplectic viewpoints on torus actions have
enriched the subject with new combinatorial ideas and methods, largely based on
the convex-geometric concept of polytopes.
The study of algebraic torus actions on algebraic varieties has quickly devel-
opedintoahighlysuccessfulbranchofalgebraicgeometry,knownastoricgeometry.
It gives a bijection between, on the one hand, toric varieties, which are complex
algebraic varieties equipped with an action of an algebraic torus with a dense or-
bit, and on the other hand, fans, which are combinatorial objects. The fan allows
onetocompletelytranslatevariousalgebraic-geometricnotionsintocombinatorics.
Projective toric varieties correspond to fans which arise from convex polytopes. A
valuable aspect of this theory is that it provides many explicit examples of alge-
braic varieties, leading to applications in deep subjects such as singularity theory
and mirror symmetry.
In symplectic geometry, since the early 1980s there has been much activity in
the field of Hamiltonian group actions on symplectic manifolds. Such an action
defines the moment map from the manifold to a Euclidean space (more precisely,
thedualLiealgebraofthetorus)whoseimageisaconvexpolytope.Ifthetorushas
half the dimension of the manifold, the image of the moment map determines the
manifold up toequivariant symplectomorphism. The class of polytopeswhich arise
astheimagesofmomentmapscanbedescribedexplicitly,togetherwithaneffective
procedureforrecoveringasymplecticmanifoldfromsuchapolytope.Insymplectic
geometry, as in algebraic geometry, one translates various geometric constructions
into the language of convex polytopes and combinatorics.
Thereisatightrelationshipbetweenthealgebraicandthesymplecticpictures:
a projective embedding of a toric manifold determines a symplectic form and a
moment map. The image of the moment map is a convex polytope that is dual to
the fan. In both the smooth algebraic-geometric and the symplectic situations, the
compact torus action is locally isomorphic to the standard action of (S1)n on Cn
by rotation of the coordinates. Thus the quotient of the manifold by this action
is naturally a manifold with corners, stratified according to the dimension of the
stabilisers, and each stratum can be equipped with data that encodes the isotropy
torusactionalongthatstratum.Notonlydoesthisstructureofthequotientprovide
a powerful means of investigating the action, but some of its subtler combinatorial
properties may also be illuminated by a careful study of the equivariant topology
ix