Contributions to the Stable Derived Categories of Gorenstein Rings
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Change of Rings Theorems
CHANG E OF RINGS THEOREMS CHANGE OF RINGS THEOREMS By PHILIP MURRAY ROBINSON, B.SC. A Thesis Submitted to the School of Graduate Studies in Partial Fulfilment of the Requirements for the Degree Master of Science McMaster University (July) 1971 MASTER OF SCIENCE (1971) l'v1cHASTER UNIVERSITY {Mathematics) Hamilton, Ontario TITLE: Change of Rings Theorems AUTHOR: Philip Murray Robinson, B.Sc. (Carleton University) SUPERVISOR: Professor B.J.Mueller NUMBER OF PAGES: v, 38 SCOPE AND CONTENTS: The intention of this thesis is to gather together the results of various papers concerning the three change of rings theorems, generalizing them where possible, and to determine if the various results, although under different hypotheses, are in fact, distinct. {ii) PREFACE Classically, there exist three theorems which relate the two homological dimensions of a module over two rings. We deal with the first and last of these theorems. J. R. Strecker and L. W. Small have significantly generalized the "Third Change of Rings Theorem" and we have simply re organized their results as Chapter 2. J. M. Cohen and C. u. Jensen have generalized the "First Change of Rings Theorem", each with hypotheses seemingly distinct from the other. However, as Chapter 3 we show that by developing new proofs for their theorems we can, indeed, generalize their results and by so doing show that their hypotheses coincide. Some examples due to Small and Cohen make up Chapter 4 as a completion to the work. (iii) ACKNOW-EDGMENTS The author expresses his sincere appreciation to his supervisor, Dr. B. J. Mueller, whose guidance and helpful criticisms were of greatest value in the preparation of this thesis. -
Topics in Module Theory
Chapter 7 Topics in Module Theory This chapter will be concerned with collecting a number of results and construc- tions concerning modules over (primarily) noncommutative rings that will be needed to study group representation theory in Chapter 8. 7.1 Simple and Semisimple Rings and Modules In this section we investigate the question of decomposing modules into \simpler" modules. (1.1) De¯nition. If R is a ring (not necessarily commutative) and M 6= h0i is a nonzero R-module, then we say that M is a simple or irreducible R- module if h0i and M are the only submodules of M. (1.2) Proposition. If an R-module M is simple, then it is cyclic. Proof. Let x be a nonzero element of M and let N = hxi be the cyclic submodule generated by x. Since M is simple and N 6= h0i, it follows that M = N. ut (1.3) Proposition. If R is a ring, then a cyclic R-module M = hmi is simple if and only if Ann(m) is a maximal left ideal. Proof. By Proposition 3.2.15, M =» R= Ann(m), so the correspondence the- orem (Theorem 3.2.7) shows that M has no submodules other than M and h0i if and only if R has no submodules (i.e., left ideals) containing Ann(m) other than R and Ann(m). But this is precisely the condition for Ann(m) to be a maximal left ideal. ut (1.4) Examples. (1) An abelian group A is a simple Z-module if and only if A is a cyclic group of prime order. -
Characterizing Gorenstein Rings Using Contracting Endomorphisms
CHARACTERIZING GORENSTEIN RINGS USING CONTRACTING ENDOMORPHISMS BRITTNEY FALAHOLA AND THOMAS MARLEY Dedicated to Craig Huneke on the occasion of his 65th birthday. Abstract. We prove several characterizations of Gorenstein rings in terms of vanishings of derived functors of certain modules or complexes whose scalars are restricted via contracting endomorphisms. These results can be viewed as analogues of results of Kunz (in the case of the Frobenius) and Avramov- Hochster-Iyengar-Yao (in the case of general contracting endomorphisms). 1. Introduction In 1969 Kunz [17] proved that a commutative Noetherian local ring of prime char- acteristic is regular if and only if some (equivalently, every) power of the Frobenius endomorphism is flat. Subsequently, the Frobenius map has been employed to great effect to study homological properties of commutative Noetherian local rings; see [20], [10], [23], [16], [4] and [3], for example. In this paper, we explore characteriza- tions of Gorenstein rings using the Frobenius map, or more generally, contracting endomorphisms. Results of this type have been obtained by Iyengar and Sather- Wagstaff [14], Goto [9], Rahmati [21], Marley [18], and others. Our primary goal is to obtain characterizations for a local ring to be Gorenstein in terms of one or more vanishings of derived functors in which one of the modules is viewed as an R-module by means of a contracting endomorphism (i.e., via restriction of scalars). A prototype of a result of this kind for regularity is given by Theorem 1.1 below. Let R be a commutative Noetherian local ring with maximal ideal m and φ : R ! R an endomorphism which is contracting, i.e., φi(m) ⊆ m2 for some i. -
Cohen-Macaulay Modules Over Gorenstein Local Rings
COHEN{MACAULAY MODULES OVER GORENSTEIN LOCAL RINGS RYO TAKAHASHI Contents Introduction 1 1. Associated primes 1 2. Depth 3 3. Krull dimension 6 4. Cohen{Macaulay rings and Gorenstein rings 9 Appendix A. Proof of Theorem 1.12 11 Appendix B. Proof of Theorem 4.8 13 References 17 Introduction Goal. The structure theorem of (maximal) Cohen{Macaulay modules over commutative Gorenstein local rings Throughout. • (R : a commutative Noetherian ring with 1 A = k[[X; Y ]]=(XY ) • k : a field B = k[[X; Y ]]=(X2;XY ) • x := X; y := Y 1. Associated primes Def 1.1. Let I ( R be an ideal of R (1) I is a maximal ideal if there exists no ideal J of R with I ( J ( R (2) I is a prime ideal if (ab 2 I ) a 2 I or b 2 I) (3) Spec R := fPrime ideals of Rg Ex 1.2. Spec A = f(x); (y); (x; y)g; Spec B = f(x); (x; y)g Prop 1.3. I ⊆ R an ideal (1) I is prime iff R=I is an integral domain (2) I is maximal iff R=I is a field 2010 Mathematics Subject Classification. 13C14, 13C15, 13D07, 13H10. Key words and phrases. Associated prime, Cohen{Macaulay module, Cohen{Macaulay ring, Ext module, Gorenstein ring, Krull dimension. 1 2 RYO TAKAHASHI (3) Every maximal ideal is prime Throughout the rest of this section, let M be an R-module. Def 1.4. p 2 Spec R is an associated prime of M if 9 x 2 M s.t p = ann(x) AssR M := fAssociated primes of Mg Ex 1.5. -
Arxiv:1802.08409V2 [Math.AC]
CORRESPONDENCE BETWEEN TRACE IDEALS AND BIRATIONAL EXTENSIONS WITH APPLICATION TO THE ANALYSIS OF THE GORENSTEIN PROPERTY OF RINGS SHIRO GOTO, RYOTARO ISOBE, AND SHINYA KUMASHIRO Abstract. Over an arbitrary commutative ring, correspondences among three sets, the set of trace ideals, the set of stable ideals, and the set of birational extensions of the base ring, are studied. The correspondences are well-behaved, if the base ring is a Gorenstein ring of dimension one. It is shown that with one extremal exception, the surjectivity of one of the correspondences characterizes the Gorenstein property of the base ring, provided it is a Cohen-Macaulay local ring of dimension one. Over a commutative Noetherian ring, a characterization of modules in which every submodule is a trace module is given. The notion of anti-stable rings is introduced, exploring their basic properties. Contents 1. Introduction 1 2. Correspondence between trace ideals and birational extensionsofthebasering 5 3. The case where R is a Gorenstein ring of dimension one 9 4. Modules in which every submodule is a trace module 13 5. Surjectivity of the correspondence ρ in dimension one 17 6. Anti-stable rings 21 References 25 1. Introduction This paper aims to explore the structure of (not necessarily Noetherian) commutative arXiv:1802.08409v2 [math.AC] 7 Dec 2018 rings in connection with their trace ideals. Let R be a commutative ring. For R-modules M and X, let τM,X : HomR(M,X) ⊗R M → X denote the R-linear map defined by τM,X (f ⊗ m) = f(m) for all f ∈ HomR(M,X) and m ∈ M. -
Gille Beamer Part 1
Torsors over affine curves Philippe Gille Institut Camille Jordan, Lyon PCMI (Utah), July 12, 2021 This is the first part The Swan-Serre correspondence I This is the correspondence between projective finite modules of finite rank and vector bundles, it arises from the case of a paracompact topological space [37]. We explicit it in the setting of affine schemes following the book of G¨ortz-Wedhorn [18, ch. 11] up to slightly different conventions. I Vector group schemes. Let R be a ring (commutative, unital). (a) Let M be an R{module. We denote by V(M) the affine R{scheme defined by V(M) = SpecSym•(M) ; it is affine over R and represents the R{functor S 7! HomS−mod (M ⊗R S; S) = HomR−mod (M; S) [11, 9.4.9]. Vector group schemes • I V(M) = Spec Sym (M) ; I It is called the vector group scheme attached to M, this construction commutes with arbitrary base change of rings R ! R0. I Proposition [32, I.4.6.1] The functor M ! V(M) induces an antiequivalence of categories between the category of R{modules and that of vector group schemes over R. An inverse functor is G 7! G(R). Vector group schemes II I (b) We assume now that M is locally free of finite rank and denote by M_ its dual. In this case Sym•(M) is of finite presentation (ibid, 9.4.11). Also the R{functor S 7! M ⊗R S is representable by the affine R{scheme V(M_) which is also denoted by W(M) [32, I.4.6]. -
Commutative Algebra
Commutative Algebra Andrew Kobin Spring 2016 / 2019 Contents Contents Contents 1 Preliminaries 1 1.1 Radicals . .1 1.2 Nakayama's Lemma and Consequences . .4 1.3 Localization . .5 1.4 Transcendence Degree . 10 2 Integral Dependence 14 2.1 Integral Extensions of Rings . 14 2.2 Integrality and Field Extensions . 18 2.3 Integrality, Ideals and Localization . 21 2.4 Normalization . 28 2.5 Valuation Rings . 32 2.6 Dimension and Transcendence Degree . 33 3 Noetherian and Artinian Rings 37 3.1 Ascending and Descending Chains . 37 3.2 Composition Series . 40 3.3 Noetherian Rings . 42 3.4 Primary Decomposition . 46 3.5 Artinian Rings . 53 3.6 Associated Primes . 56 4 Discrete Valuations and Dedekind Domains 60 4.1 Discrete Valuation Rings . 60 4.2 Dedekind Domains . 64 4.3 Fractional and Invertible Ideals . 65 4.4 The Class Group . 70 4.5 Dedekind Domains in Extensions . 72 5 Completion and Filtration 76 5.1 Topological Abelian Groups and Completion . 76 5.2 Inverse Limits . 78 5.3 Topological Rings and Module Filtrations . 82 5.4 Graded Rings and Modules . 84 6 Dimension Theory 89 6.1 Hilbert Functions . 89 6.2 Local Noetherian Rings . 94 6.3 Complete Local Rings . 98 7 Singularities 106 7.1 Derived Functors . 106 7.2 Regular Sequences and the Koszul Complex . 109 7.3 Projective Dimension . 114 i Contents Contents 7.4 Depth and Cohen-Macauley Rings . 118 7.5 Gorenstein Rings . 127 8 Algebraic Geometry 133 8.1 Affine Algebraic Varieties . 133 8.2 Morphisms of Affine Varieties . 142 8.3 Sheaves of Functions . -
Arxiv:Math/0301347V1
Contemporary Mathematics Morita Contexts, Idempotents, and Hochschild Cohomology — with Applications to Invariant Rings — Ragnar-Olaf Buchweitz Dedicated to the memory of Peter Slodowy Abstract. We investigate how to compare Hochschild cohomology of algebras related by a Morita context. Interpreting a Morita context as a ring with distinguished idempotent, the key ingredient for such a comparison is shown to be the grade of the Morita defect, the quotient of the ring modulo the ideal generated by the idempotent. Along the way, we show that the grade of the stable endomorphism ring as a module over the endomorphism ring controls vanishing of higher groups of selfextensions, and explain the relation to various forms of the Generalized Nakayama Conjecture for Noetherian algebras. As applications of our approach we explore to what extent Hochschild cohomology of an invariant ring coincides with the invariants of the Hochschild cohomology. Contents Introduction 1 1. Morita Contexts 3 2. The Grade of the Stable Endomorphism Ring 6 3. Equivalences to the Generalized Nakayama Conjecture 12 4. The Comparison Homomorphism for Hochschild Cohomology 14 5. Hochschild Cohomology of Auslander Contexts 17 6. Invariant Rings: The General Case 20 7. Invariant Rings: The Commutative Case 23 References 27 arXiv:math/0301347v1 [math.AC] 29 Jan 2003 Introduction One of the basic features of Hochschild (co-)homology is its invariance under derived equivalence, see [25], in particular, it is invariant under Morita equivalence, a result originally established by Dennis-Igusa [18], see also [26]. This raises the question how Hochschild cohomology compares in general for algebras that are just ingredients of a Morita context. -
Ideals Generated by Pfaffians P(P, 72) =
CORE Metadata, citation and similar papers at core.ac.uk Provided by Elsevier - Publisher Connector Ideals Generated by Pfaffians Instituie of .lfatlrenzatics, Polish Academy of Sciences, CJropinu 12, 87-100 Torwi, Poland AND PIOTR PRAGACZ Institute of Mathematics, Nicholas Copernicus University, Chopina 12, 87-100 Ton&, Poland Communicated by D. Buchsbaum Received September 7, 1978 Influenced by the structure theorem of Buchsbaum and Eisenbud for Gorenstein ideals of depth 3, [4], we study in this paper ideals generated by Pfaffians of given order of an alternating matrix. Let ,x7 be an n by n alternating matrix (i.e., xi9 = --xji for i < j and xii = 0) with entries in a commutative ring R with identity. One can associate with X an element Pf(-k-) of R called Pfaffian of X (see [I] or [2] for the definition). For n odd det S ~-=0 and Pf(X) = 0; for n even det X is a square in R and Pf(X)z = det X. For a basis-free account and basic properties ofpfaffians we send interested readers to Chapter 2 of [4] or to [IO]. For a sequence i1 ,..., &, 1 < i r < n, the matrix obtained from X by omitting rows and columns with indices i1 ,..., ik is again alternating; we write Pf il*....ik(X) for its Pfaffian and call it the (n - k)-order Pfaffian of X. We are interested in ideals Pf,,(X) generated by all the 2p-order Pfaffians of X, 0 ,( 2p < n. After some preliminaries in Section 1 we prove in Section 2 that the height and the depth of E-“&X) are bounded by the number P(P, 72) = (12- 2p + l)(n - 2p + 2)/2. -
Gorenstein Rings Examples References
Origin Aim of the Thesis Structure of Minimal Injective Resolution Gorenstein Rings Examples References Gorenstein Rings Chau Chi Trung Bachelor Thesis Defense Presentation Supervisor: Dr. Tran Ngoc Hoi University of Science - Vietnam National University Ho Chi Minh City May 2018 Email: [email protected] Origin Aim of the Thesis Structure of Minimal Injective Resolution Gorenstein Rings Examples References Content 1 Origin 2 Aim of the Thesis 3 Structure of Minimal Injective Resolution 4 Gorenstein Rings 5 Examples 6 References Origin ∙ Grothendieck introduced the notion of Gorenstein variety in algebraic geometry. ∙ Serre made a remark that rings of finite injective dimension are just Gorenstein rings. The remark can be found in [9]. ∙ Gorenstein rings have now become a popular notion in commutative algebra and given birth to several definitions such as nearly Gorenstein rings or almost Gorenstein rings. Aim of the Thesis This thesis aims to 1 present basic results on the minimal injective resolution of a module over a Noetherian ring, 2 introduce Gorenstein rings via Bass number and 3 answer elementary questions when one inspects a type of ring (e.g. Is a subring of a Gorenstein ring Gorenstein?). Origin Aim of the Thesis Structure of Minimal Injective Resolution Gorenstein Rings Examples References Structure of Minimal Injective Resolution Unless otherwise specified, let R be a Noetherian commutative ring with 1 6= 0 and M be an R-module. Theorem (E. Matlis) Let E be a nonzero injective R-module. Then we have a direct sum ∼ decomposition E = ⊕i2I Xi in which for each i 2 I, Xi = ER(R=P ) for some P 2 Spec(R). -
Galois Extensions of Structured Ring Spectra 3
GALOIS EXTENSIONS OF STRUCTURED RING SPECTRA John Rognes August 31st 2005 Abstract. We introduce the notion of a Galois extension of commutative S-algebras (E∞ ring spectra), often localized with respect to a fixed homology theory. There are numerous examples, including some involving Eilenberg–MacLane spectra of commutative rings, real and complex topological K-theory, Lubin–Tate spectra and cochain S-algebras. We establish the main theorem of Galois theory in this general- ity. Its proof involves the notions of separable and ´etale extensions of commutative S-algebras, and the Goerss–Hopkins–Miller theory for E∞ mapping spaces. We show that the global sphere spectrum S is separably closed, using Minkowski’s discrimi- nant theorem, and we estimate the separable closure of its localization with respect to each of the Morava K-theories. We also define Hopf–Galois extensions of com- mutative S-algebras, and study the complex cobordism spectrum MU as a common integral model for all of the local Lubin–Tate Galois extensions. Contents 1. Introduction 2. Galois extensions in algebra 2.1. Galois extensions of fields 2.2. Regular covering spaces 2.3. Galois extensions of commutative rings 3. Closed categories of structured module spectra 3.1. Structured spectra arXiv:math/0502183v2 [math.AT] 6 Dec 2005 3.2. Localized categories 3.3. Dualizable spectra 3.4. Stably dualizable groups 3.5. The dualizing spectrum 3.6. The norm map 4. Galois extensions in topology 4.1. Galois extensions of E-local commutative S-algebras 4.2. The Eilenberg–Mac Lane embedding 4.3. Faithful extensions 5. -
Complex Oriented Cohomology Theories and the Language of Stacks
COMPLEX ORIENTED COHOMOLOGY THEORIES AND THE LANGUAGE OF STACKS COURSE NOTES FOR 18.917, TAUGHT BY MIKE HOPKINS Contents Introduction 1 1. Complex Oriented Cohomology Theories 2 2. Formal Group Laws 4 3. Proof of the Symmetric Cocycle Lemma 7 4. Complex Cobordism and MU 11 5. The Adams spectral sequence 14 6. The Hopf Algebroid (MU∗; MU∗MU) and formal groups 18 7. More on isomorphisms, strict isomorphisms, and π∗E ^ E: 22 8. STACKS 25 9. Stacks and Associated Stacks 29 10. More on Stacks and associated stacks 32 11. Sheaves on stacks 36 12. A calculation and the link to topology 37 13. Formal groups in prime characteristic 40 14. The automorphism group of the Lubin-Tate formal group laws 46 15. Formal Groups 48 16. Witt Vectors 50 17. Classifying Lifts | The Lubin-Tate Space 53 18. Cohomology of stacks, with applications 59 19. p-typical Formal Group Laws. 63 20. Stacks: what's up with that? 67 21. The Landweber exact functor theorem 71 References 74 Introduction This text contains the notes from a course taught at MIT in the spring of 1999, whose topics revolved around the use of stacks in studying complex oriented cohomology theories. The notes were compiled by the graduate students attending the class, and it should perhaps be acknowledged (with regret) that we recorded only the mathematics and not the frequent jokes and amusing sideshows which accompanied it. Please be wary of the fact that what you have in your hands is the `alpha- version' of the text, which is only slightly more than our direct transcription of the stream-of- consciousness lectures.