DOCSLIB.ORG

Characteristic P Techniques in Commutative Algebra and Algebraic Geometry Math 732 - Winter 2019

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Characteristic P Techniques in Commutative Algebra and Algebraic Geometry Math 732 - Winter 2019 Characteristic p Techniques in Commutative Algebra and Algebraic Geometry Math 732 - Winter 2019 Karen E Smith1 Department of Mathematics, University of Michigan, Ann Arbor, MI 48109 E-mail address: [email protected] 1Acknowledgements: These notes loosely follow notes by Karl Schwede for a course on similar topics in Spring 2017 at the University of Utah. The arguments in Chapter 1, Section 3 draw heavily from notes of Mel Hochster. The section on Fedder's Criterion draws heavily from Karl's notes. Preface The goal of this course is to introduce the Frobenius morphism and its uses in commutative algebra and algebraic geometry. These characteristic p techniques have been used in commutative algebra, for example, to establish that certain rings are Cohen-Macaulay, as in the famous Hochster-Roberts theorem for rings of invariants (over fields of arbitrary character- istic). In more geometric settings, characteristic p techniques can help analyze or quantify how singular|that is, how far from being smooth|a particular variety may be, or to establish that the singularities are suitably mild. Vast bodies of research in birational algebraic geometry that had been developed for complex varieties using differential forms and L2-techniques have now been seen to have \characteristic p" analogs. These can be used to recover much of the theory in the complex setting, but even better, can serve as replacements to the analytic techniques to establish results for varieties of prime characteristic p. Examples of such analogs we will discuss in this course include the F-pure threshold and test ideals, which are \characteristic p analogs" of the log canonical threshold and multiplier ideals in complex geometry. In this course, we will introduce this machinery, while also introducing and/or re- viewing many of the sub-areas of commutative algebra and algebraic geometry where it has been useful. We begin with Kunz's characterization of regularity (smooth- ness) as the flatness of Frobenius. First, of course, we review regular local rings more broadly, including Serre's famous characterization in terms of global dimension. From there, we will consider classes of \mild singularities" for complex varieties, review- ing the definitions of rational, log canonical and log terminal singularities which are defined using resolutions of singularities. These all have \characteristic p analogs" defined using Frobenius, which we will explore in depth. We will then study some global implications of Frobenius splitting, including vanishing theorems for line bun- dles and characterizations of Fano (or nearly Fano) varieties. As time and student interest permit, we may study singularity invariants such as the log canonical thresh- old and its \characteristic p analog" called the F-pure threshold, as well as multiplier and test ideals, Hilbert-Kunz Multiplicity and/or F-signature. CHAPTER 1 Introduction 1. Overview Let X be a Noetherian scheme of prime characteristic p. The Frobenius mor- phism is the scheme map F : X ! X OX ! F∗OX which is the identity map on the underlying topological space X but the pth power map on sections. For example, when X = Spec R is affine, the Frobenius map is essentially just the ring homomorphism R ! R sending r 7! rp. An important special case to keep in mind is the case where X is a variety over an algebraically closed field K of characteristic p > 0. The Frobenius map is a powerful tool, both in commutative algebra and algebraic geometry. Some of its uses include (a) Detecting regularity of X: A famous theorem of Kunz says that X is regular if and only if the Frobenius morphism is flat. For varieties, this says that X is smooth if and only if F∗OX is a locally free sheaf (or vector bundle). (b) By relaxing the flatness condition for the Frobenius in various ways, we get a host of other \mild singularity" classes in prime characteristic, with names you may have heard before such as F-regular and F-pure. Many theorems that hold for smooth varieties over fields of characteristic p can be extended to these classes of \F-singularities." (c) Frobenius can be used to detect \mild" singularities of complex varieties as well. Singularities of importance in complex birational geometry such as Kawamata log terminal or canonical singularities can be understood by \reduction to prime characteristic," where surprisingly checkable criteria for these singularities can be given in terms of the Frobenius map. (d) In commutative algebra, the Frobenius can be used to proving certain rings are Cohen-Macaulay or have other nice properties. Again, by reduction to prime characteristic, such techniques can be applied to any ring containing a field. (e) The Frobenius map can be used to prove vanishing theorems for cohomology of line bundles on varieties of prime characteristic under certain conditions. Thus Frobenius can often be used when resolution of singularities, Kodaira Vanishing, or other tools fail (or are unknown) in characteristic p. 3 4 1. INTRODUCTION (f) Frobenius can be used to define numerical invariants of singularities. For example, the F-pure threshold is an invariant defined using the Frobenius which is an analog of the analytic index of singularities (or log canonical threshold) for complex varieties. A smooth point on a hypersurface always has F-pure threshold 1, but singular points have smaller (positive) thresholds| the smaller, the more singular. As one concrete example, consider the simple cusp defined by y2 = x3. This singularity has F-pure threshold equal to 1=2 in char 2 2=3 in char 3 5 1 6 − 6p if char p = 5 mod 6 5 6 if char p = 1 mod 6: This reflects the fact that the cusp is somehow most singular in characteristic 2, slightly less singular in characteristic 3, and increasing less singular for large p. For infinitely many p (namely, those p congruent to 5 mod 6), it it is not really anymore singular than it is over complex numbers, in the sense that the log canonical threshold of the cusp over C is also 5=6. The fact that the cusp is \more singular" in some characteristics, even infinitely many, than it is over C is deeply connected to arithmetic issues related to supersingularity for elliptic curves. Here is one specific long-standing conjecture: for a given polynomial with integer coefficients (say), the log canonical threshold of the corresponding hypersurface over C is equal to the F-pure threshold of the hypersurface considered over Fp for infinitely many p. Our goal will be to expand on all of these topics over the semester. 1.0.1. Local Properties. Let P be a property of schemes (or, say, of varieties or of topological spaces). We say that \P is a local property" if for any scheme X, X has property P if and only if for all x 2 X, there is an open neighborhood U where property P holds. Note the locus X0 of points of an arbitrary scheme X where the local property P holds will be an open set of X. For example, smoothness and normality are both local properties of complex varieties. Any property characterizing the `singularities' of a scheme ought to be a local property. Typically, a property of a scheme X may be defined in terms of ring properties for its stalks OX;x. That is, we may say that a point x has property P if and only if the stalk OX;x has property P. Reducedness and normality are such a properties of schemes, as are more exotic properties such as Cohen-Macaulayness and Gorenstein- ness. Property P holding for X if and only if it holds for all points x 2 X follows immediately if P is a local property, but this is weaker assumption in general. Note that if P is such a local property and some stalk OX;x has property P, then all further localizations OX;y must have property P. Indeed, to say that OX;y is a further localization of OX;x is to say that the point x is in the closure of y, so every open set containing x will also contain y. 1. OVERVIEW 5 Non-local properties include connectedness, or the property that the sheaf !X has a non-zero section. It is not always obvious whether or not a given property is local, even when we expect it to be. For example, the property of regularity for Noetherian schemes, introduced mid-last century as a scheme analog of smoothness for algebraic varieties, was long expected to be a local property. However, until the advent of homological algebra, it wasn't even known that a localization of a regular local ring is regular; this was settled in the 1950's by Serre (and independently Auslander-Buchsbaum) who gave new homological characterizations of regularity. Unfortunately, it turns out that regularity is not a local property [Hoc], though it is for large classes of rings with mild hypothesis. CHAPTER 2 Regularity and Kunz's theorem 1. Frobenius We begin with the \local" picture, studying Frobenius for rings. Setting 1.1. The word \ring" in these notes always means a commutative ring with unity (unless explicitly stated otherwise). Our rings are usually Noetherian. Recall that a Noetherian ring is called local if it has a unique maximal ideal. The notation (R; m; K) will always denote a Noetherian local ring with maximal ideal m and residue field K = R=m. We start with some examples of the types of rings we are interested in. Example 1.2. (a) The polynomial ring C[x1; : : : ; xn]; this is the ring of polyno- mial (or regular) functions on the variety Cn.
Load more

Recommended publications
  • Arxiv:1108.5351V3 [Math.AG] 26 Oct 2012 ..Rslso D-Mod( on Results Introduction the to 0.2
    ON SOME FINITENESS QUESTIONS FOR ALGEBRAIC STACKS VLADIMIR DRINFELD AND DENNIS GAITSGORY Abstract. We prove that under a certain mild hypothesis, the DG category of D-modules on a quasi-compact algebraic stack is compactly generated. We also show that under the same hypothesis, the functor of global sections on the DG category of quasi-coherent sheaves is continuous. Contents Introduction 3 0.1. Introduction to the introduction 3 0.2. Results on D-mod(Y) 4 0.3. Results on QCoh(Y) 4 0.4. Ind-coherent sheaves 5 0.5. Contents of the paper 7 0.6. Conventions, notation and terminology 10 0.7. Acknowledgments 14 1. Results on QCoh(Y) 14 1.1. Assumptions on stacks 14 1.2. Quasi-coherent sheaves 15 1.3. Direct images for quasi-coherent sheaves 18 1.4. Statements of the results on QCoh(Y) 21 2. Proof of Theorems 1.4.2 and 1.4.10 23 2.1. Reducing the statement to a key lemma 23 2.2. Easy reduction steps 24 2.3. Devissage 24 2.4. Quotients of schemes by algebraic groups 26 2.5. Proof of Proposition 2.3.4 26 2.6. Proof of Theorem 1.4.10 29 arXiv:1108.5351v3 [math.AG] 26 Oct 2012 3. Implications for ind-coherent sheaves 30 3.1. The “locally almost of finite type” condition 30 3.2. The category IndCoh 32 3.3. The coherent subcategory 39 3.4. Description of compact objects of IndCoh(Y) 39 3.5. The category Coh(Y) generates IndCoh(Y) 42 3.6.
    [Show full text]
  • On Free Quasigroups and Quasigroup Representations Stefanie Grace Wang Iowa State University
    Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2017 On free quasigroups and quasigroup representations Stefanie Grace Wang Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Mathematics Commons Recommended Citation Wang, Stefanie Grace, "On free quasigroups and quasigroup representations" (2017). Graduate Theses and Dissertations. 16298. https://lib.dr.iastate.edu/etd/16298 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. On free quasigroups and quasigroup representations by Stefanie Grace Wang A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Mathematics Program of Study Committee: Jonathan D.H. Smith, Major Professor Jonas Hartwig Justin Peters Yiu Tung Poon Paul Sacks The student author and the program of study committee are solely responsible for the content of this dissertation. The Graduate College will ensure this dissertation is globally accessible and will not permit alterations after a degree is conferred. Iowa State University Ames, Iowa 2017 Copyright c Stefanie Grace Wang, 2017. All rights reserved. ii DEDICATION I would like to dedicate this dissertation to the Integral Liberal Arts Program. The Program changed my life, and I am forever grateful. It is as Aristotle said, \All men by nature desire to know." And Montaigne was certainly correct as well when he said, \There is a plague on Man: his opinion that he knows something." iii TABLE OF CONTENTS LIST OF TABLES .
    [Show full text]
  • Formal Power Series - Wikipedia, the Free Encyclopedia
    Formal power series - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Formal_power_series Formal power series From Wikipedia, the free encyclopedia In mathematics, formal power series are a generalization of polynomials as formal objects, where the number of terms is allowed to be infinite; this implies giving up the possibility to substitute arbitrary values for indeterminates. This perspective contrasts with that of power series, whose variables designate numerical values, and which series therefore only have a definite value if convergence can be established. Formal power series are often used merely to represent the whole collection of their coefficients. In combinatorics, they provide representations of numerical sequences and of multisets, and for instance allow giving concise expressions for recursively defined sequences regardless of whether the recursion can be explicitly solved; this is known as the method of generating functions. Contents 1 Introduction 2 The ring of formal power series 2.1 Definition of the formal power series ring 2.1.1 Ring structure 2.1.2 Topological structure 2.1.3 Alternative topologies 2.2 Universal property 3 Operations on formal power series 3.1 Multiplying series 3.2 Power series raised to powers 3.3 Inverting series 3.4 Dividing series 3.5 Extracting coefficients 3.6 Composition of series 3.6.1 Example 3.7 Composition inverse 3.8 Formal differentiation of series 4 Properties 4.1 Algebraic properties of the formal power series ring 4.2 Topological properties of the formal power series
    [Show full text]
  • NOTES on CARTIER and WEIL DIVISORS Recall: Definition 0.1. A
    NOTES ON CARTIER AND WEIL DIVISORS AKHIL MATHEW Abstract. These are notes on divisors from Ravi Vakil's book [2] on scheme theory that I prepared for the Foundations of Algebraic Geometry seminar at Harvard. Most of it is a rewrite of chapter 15 in Vakil's book, and the originality of these notes lies in the mistakes. I learned some of this from [1] though. Recall: Definition 0.1. A line bundle on a ringed space X (e.g. a scheme) is a locally free sheaf of rank one. The group of isomorphism classes of line bundles is called the Picard group and is denoted Pic(X). Here is a standard source of line bundles. 1. The twisting sheaf 1.1. Twisting in general. Let R be a graded ring, R = R0 ⊕ R1 ⊕ ::: . We have discussed the construction of the scheme ProjR. Let us now briefly explain the following additional construction (which will be covered in more detail tomorrow). L Let M = Mn be a graded R-module. Definition 1.1. We define the sheaf Mf on ProjR as follows. On the basic open set D(f) = SpecR(f) ⊂ ProjR, we consider the sheaf associated to the R(f)-module M(f). It can be checked easily that these sheaves glue on D(f) \ D(g) = D(fg) and become a quasi-coherent sheaf Mf on ProjR. Clearly, the association M ! Mf is a functor from graded R-modules to quasi- coherent sheaves on ProjR. (For R reasonable, it is in fact essentially an equiva- lence, though we shall not need this.) We now set a bit of notation.
    [Show full text]
  • MAPPING STACKS and CATEGORICAL NOTIONS of PROPERNESS Contents 1. Introduction 2 1.1. Introduction to the Introduction 2 1.2
    MAPPING STACKS AND CATEGORICAL NOTIONS OF PROPERNESS DANIEL HALPERN-LEISTNER AND ANATOLY PREYGEL Abstract. One fundamental consequence of a scheme being proper is that there is an algebraic space classifying maps from it to any other finite type scheme, and this result has been extended to proper stacks. We observe, however, that it also holds for many examples where the source is a geometric stack, such as a global quotient. In our investigation, we are lead naturally to certain properties of the derived category of a stack which guarantee that the mapping stack from it to any geometric finite type stack is algebraic. We develop methods for establishing these properties in a large class of examples. Along the way, we introduce a notion of projective morphism of algebraic stacks, and prove strong h-descent results which hold in the setting of derived algebraic geometry but not in classical algebraic geometry. Contents 1. Introduction 2 1.1. Introduction to the introduction2 1.2. Mapping out of stacks which are \proper enough"3 1.3. Techniques for establishing (GE) and (L)5 1.4. A long list of examples6 1.5. Comparison with previous results7 1.6. Notation and conventions8 1.7. Author's note 9 2. Artin's criteria for mapping stacks 10 2.1. Weil restriction of affine stacks 11 2.2. Deformation theory of the mapping stack 12 2.3. Integrability via the Tannakian formalism 16 2.4. Derived representability from classical representability 19 2.5. Application: (pGE) and the moduli of perfect complexes 21 3. Perfect Grothendieck existence 23 3.1.
    [Show full text]
  • The Smooth Locus in Infinite-Level Rapoport-Zink Spaces
    The smooth locus in infinite-level Rapoport-Zink spaces Alexander Ivanov and Jared Weinstein February 25, 2020 Abstract Rapoport-Zink spaces are deformation spaces for p-divisible groups with additional structure. At infinite level, they become preperfectoid spaces. Let M8 be an infinite-level Rapoport-Zink space of ˝ ˝ EL type, and let M8 be one connected component of its geometric fiber. We show that M8 contains a dense open subset which is cohomologically smooth in the sense of Scholze. This is the locus of p-divisible groups which do not have any extra endomorphisms. As a corollary, we find that the cohomologically smooth locus in the infinite-level modular curve Xpp8q˝ is exactly the locus of elliptic curves E with supersingular reduction, such that the formal group of E has no extra endomorphisms. 1 Main theorem Let p be a prime number. Rapoport-Zink spaces [RZ96] are deformation spaces of p-divisible groups equipped with some extra structure. This article concerns the geometry of Rapoport-Zink spaces of EL type (endomor- phisms + level structure). In particular we consider the infinite-level spaces MD;8, which are preperfectoid spaces [SW13]. An example is the space MH;8, where H{Fp is a p-divisible group of height n. The points of MH;8 over a nonarchimedean field K containing W pFpq are in correspondence with isogeny classes of p-divisible groups G{O equipped with a quasi-isogeny G b O {p Ñ H b O {p and an isomorphism K OK K Fp K n Qp – VG (where VG is the rational Tate module).
    [Show full text]
  • Bertini's Theorem on Generic Smoothness
    U.F.R. Mathematiques´ et Informatique Universite´ Bordeaux 1 351, Cours de la Liberation´ Master Thesis in Mathematics BERTINI1S THEOREM ON GENERIC SMOOTHNESS Academic year 2011/2012 Supervisor: Candidate: Prof.Qing Liu Andrea Ricolfi ii Introduction Bertini was an Italian mathematician, who lived and worked in the second half of the nineteenth century. The present disser- tation concerns his most celebrated theorem, which appeared for the first time in 1882 in the paper [5], and whose proof can also be found in Introduzione alla Geometria Proiettiva degli Iperspazi (E. Bertini, 1907, or 1923 for the latest edition). The present introduction aims to informally introduce Bertini’s Theorem on generic smoothness, with special attention to its re- cent improvements and its relationships with other kind of re- sults. Just to set the following discussion in an historical perspec- tive, recall that at Bertini’s time the situation was more or less the following: ¥ there were no schemes, ¥ almost all varieties were defined over the complex numbers, ¥ all varieties were embedded in some projective space, that is, they were not intrinsic. On the contrary, this dissertation will cope with Bertini’s the- orem by exploiting the powerful tools of modern algebraic ge- ometry, by working with schemes defined over any field (mostly, but not necessarily, algebraically closed). In addition, our vari- eties will be thought of as abstract varieties (at least when over a field of characteristic zero). This fact does not mean that we are neglecting Bertini’s original work, containing already all the rele- vant ideas: the proof we shall present in this exposition, over the complex numbers, is quite close to the one he gave.
    [Show full text]
  • Sheaves with Values in a Category7
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Topology Vol. 3, pp. l-18, Pergamon Press. 196s. F’rinted in Great Britain SHEAVES WITH VALUES IN A CATEGORY7 JOHN W. GRAY (Received 3 September 1963) $4. IN’IXODUCTION LET T be a topology (i.e., a collection of open sets) on a set X. Consider T as a category in which the objects are the open sets and such that there is a unique ‘restriction’ morphism U -+ V if and only if V c U. For any category A, the functor category F(T, A) (i.e., objects are covariant functors from T to A and morphisms are natural transformations) is called the category ofpresheaces on X (really, on T) with values in A. A presheaf F is called a sheaf if for every open set UE T and for every strong open covering {U,) of U(strong means {U,} is closed under finite, non-empty intersections) we have F(U) = Llim F( U,) (Urn means ‘generalized’ inverse limit. See $4.) The category S(T, A) of sheares on X with values in A is the full subcategory (i.e., morphisms the same as in F(T, A)) determined by the sheaves. In this paper we shall demonstrate several properties of S(T, A): (i) S(T, A) is left closed in F(T, A). (Theorem l(i), $8). This says that if a left limit (generalized inverse limit) of sheaves exists as a presheaf then that presheaf is a sheaf.
    [Show full text]
  • Separable Commutative Rings in the Stable Module Category of Cyclic Groups
    SEPARABLE COMMUTATIVE RINGS IN THE STABLE MODULE CATEGORY OF CYCLIC GROUPS PAUL BALMER AND JON F. CARLSON Abstract. We prove that the only separable commutative ring-objects in the stable module category of a finite cyclic p-group G are the ones corresponding to subgroups of G. We also describe the tensor-closure of the Kelly radical of the module category and of the stable module category of any finite group. Contents Introduction1 1. Separable ring-objects4 2. The Kelly radical and the tensor6 3. The case of the group of prime order 14 4. The case of the general cyclic group 16 References 18 Introduction Since 1960 and the work of Auslander and Goldman [AG60], an algebra A over op a commutative ring R is called separable if A is projective as an A ⊗R A -module. This notion turns out to be remarkably important in many other contexts, where the module category C = R- Mod and its tensor ⊗ = ⊗R are replaced by an arbitrary tensor category (C; ⊗). A ring-object A in such a category C is separable if multiplication µ : A⊗A ! A admits a section σ : A ! A⊗A as an A-A-bimodule in C. See details in Section1. Our main result (Theorem 4.1) concerns itself with modular representation theory of finite groups: Main Theorem. Let | be a separably closed field of characteristic p > 0 and let G be a cyclic p-group. Let A be a commutative and separable ring-object in the stable category |G- stmod of finitely generated |G-modules modulo projectives.
    [Show full text]
  • LIE ALGEBRAS of CHARACTERISTIC P
    LIE ALGEBRAS OF CHARACTERISTIC p BY IRVING KAPLANSKY(') 1. Introduction. Recent publications have exhibited an amazingly large number of simple Lie algebras of characteristic p. At this writing one cannot envisage a structure theory encompassing them all; perhaps it is not even sensible to seek one. Seligman [3] picked out a subclass corresponding almost exactly to the simple Lie algebras of characteristic 0. He postulated restrictedness and the possession of a nonsingular invariant form arising from a restricted repre- sentation. In this paper our main purpose is to weaken his hypotheses by omitting the assumption that the form arises from a representation. We find no new algebras for ranks one and two. On the other hand, it is known that new algebras of this kind do exist for rank three, and at that level the in- vestigation will probably become more formidable. For rank one we are able to prove more. Just on the assumption of a non- singular invariant form we find only the usual three-dimensional algebra to be possible. Assuming simplicity and restrictedness permits in addition the survival of the Witt algebra. Still further information on algebras of rank one is provided by Theorems 1, 2 and 4. Characteristics two and three are exceptions to nearly all the results. In those two cases we are sometimes able to prove more, sometimes less; for the reader's convenience, these theorems are assembled in an appendix. In addi- tion, characteristic five is a (probably temporary) exception in Theorem 7. Two remarks on style, (a) Several proofs are broken up into a series of lemmas.
    [Show full text]
  • 4. Coherent Sheaves Definition 4.1. If (X,O X) Is a Locally Ringed Space
    4. Coherent Sheaves Definition 4.1. If (X; OX ) is a locally ringed space, then we say that an OX -module F is locally free if there is an open affine cover fUig of X such that FjUi is isomorphic to a direct sum of copies of OUi . If the number of copies r is finite and constant, then F is called locally free of rank r (aka a vector bundle). If F is locally free of rank one then we way say that F is invertible (aka a line bundle). The group of all invertible sheaves under tensor product, denoted Pic(X), is called the Picard group of X. A sheaf of ideals I is any OX -submodule of OX . Definition 4.2. Let X = Spec A be an affine scheme and let M be an A-module. M~ is the sheaf which assigns to every open subset U ⊂ X, the set of functions a s: U −! Mp; p2U which can be locally represented at p as a=g, a 2 M, g 2 R, p 2= Ug ⊂ U. Lemma 4.3. Let A be a ring and let M be an A-module. Let X = Spec A. ~ (1) M is a OX -module. ~ (2) If p 2 X then Mp is isomorphic to Mp. ~ (3) If f 2 A then M(Uf ) is isomorphic to Mf . Proof. (1) is clear and the rest is proved mutatis mutandis as for the structure sheaf. Definition 4.4. An OX -module F on a scheme X is called quasi- coherent if there is an open cover fUi = Spec Aig by affines and ~ isomorphisms FjUi ' Mi, where Mi is an Ai-module.
    [Show full text]
  • UC Berkeley UC Berkeley Electronic Theses and Dissertations
    UC Berkeley UC Berkeley Electronic Theses and Dissertations Title Cox Rings and Partial Amplitude Permalink https://escholarship.org/uc/item/7bs989g2 Author Brown, Morgan Veljko Publication Date 2012 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California Cox Rings and Partial Amplitude by Morgan Veljko Brown A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Mathematics in the Graduate Division of the University of California, BERKELEY Committee in charge: Professor David Eisenbud, Chair Professor Martin Olsson Professor Alistair Sinclair Spring 2012 Cox Rings and Partial Amplitude Copyright 2012 by Morgan Veljko Brown 1 Abstract Cox Rings and Partial Amplitude by Morgan Veljko Brown Doctor of Philosophy in Mathematics University of California, BERKELEY Professor David Eisenbud, Chair In algebraic geometry, we often study algebraic varieties by looking at their codimension one subvarieties, or divisors. In this thesis we explore the relationship between the global geometry of a variety X over C and the algebraic, geometric, and cohomological properties of divisors on X. Chapter 1 provides background for the results proved later in this thesis. There we give an introduction to divisors and their role in modern birational geometry, culminating in a brief overview of the minimal model program. In chapter 2 we explore criteria for Totaro's notion of q-amplitude. A line bundle L on X is q-ample if for every coherent sheaf F on X, there exists an integer m0 such that m ≥ m0 implies Hi(X; F ⊗ O(mL)) = 0 for i > q.
    [Show full text]