Algebraic Geometry of Curves
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
THE CUBIC THREEFOLD and FRIENDS 1. Background On
THE CUBIC THREEFOLD AND FRIENDS 1. Background on Threefolds Fano, around the 1910s, proved that any smooth quartic threefold • is not rational. Later on, in the 1950s, Roth criticised the proof as incomplete. In 1971, Iskovskikh and Manin provide a complete proof. In 1972, Artin and Mumford gave an example of another unirational, • but not rational Fano threefold. This is a certain double cover X of P3 ramified over a singular quartic surface. They showed that H3(X; Z) is a birational invariant and obtained that H3(X; Z) = Z2, from which they concluded that X cannot be rational. At the same time, Clemens and Griffiths showed that any smooth • cubic threefold V over a field of characteristic zero is unirational, but not rational. In the same year, Murre proved the result in char- acteristic p. The idea of Clemens and Griffiths was to consider two auxiliary varieties of a smooth cubic threefold V: The intermediate Jacobian J(V) - a principally polarised abelian variety • playing a role similar to that of the Jacobian for studying divisors on curves. the Fano variety of lines F(V) - a smooth projective surface parametris- • ing lines on V. In order to arrive at the result, they represented J(V) as the Albanese variety of F(V), and studied its theta divisors. 2. The Cohomology of the Cubic Threefold As before, let V be a cubic threefold, i.e. a hypersurface of degree three in P4. A first idea is to compare the cohomology of V with that of P3 and hope that we shall thus find a birational invariant that has different values for V and P3, respectively. -
Moduli Spaces of Quadratic Rational Maps with a Marked Periodic Point
J. Blanc et al. (2015) “Quadratic Maps with a Marked Periodic Point of Small Order,” International Mathematics Research Notices, Vol. 2015, No. 23, pp. 12459–12489 Advance Access Publication March 10, 2015 doi:10.1093/imrn/rnv063 Moduli Spaces of Quadratic Rational Maps with a Marked Periodic Point of Small Order Downloaded from https://academic.oup.com/imrn/article/2015/23/12459/672405 by guest on 27 September 2021 Jer´ emy´ Blanc1, Jung Kyu Canci1, and Noam D. Elkies2 1Mathematisches Institut, Universitat¨ Basel, Spiegelgasse 1, CH-4051 Basel, Switzerland and 2Department of Mathematics, Harvard University, Cambridge, MA 02138, USA Correspondence to be sent to: [email protected] The surface corresponding to the moduli space of quadratic endomorphisms of P1 with a marked periodic point of order nis studied. It is shown that the surface is rational over Q when n≤ 5 and is of general type for n= 6. An explicit description of the n= 6 surface lets us find several infinite families of quadratic endomorphisms f : P1 → P1 defined over Q with a rational periodic point of order 6. In one of these families, f also has a rational fixed point, for a total of at least 7 periodic and 7 preperiodic points. This is in contrast with the polynomial case, where it is conjectured that no polynomial endomorphism defined over Q admits rational periodic points of order n> 3. 1 Introduction A classical question in arithmetic dynamics concerns periodic, and more generally preperiodic, points of a rational map (endomorphism) f : P1(Q) → P1(Q).Apointp is said to be periodic of order n if f n(p) = p and if f i(p) = p for 0 < i < n.Apointp is said to be preperiodic if there exists a non-negative integer m such that the point f m(p) is periodic. -
INTRODUCTION to ALGEBRAIC GEOMETRY, CLASS 25 Contents 1
INTRODUCTION TO ALGEBRAIC GEOMETRY, CLASS 25 RAVI VAKIL Contents 1. The genus of a nonsingular projective curve 1 2. The Riemann-Roch Theorem with Applications but No Proof 2 2.1. A criterion for closed immersions 3 3. Recap of course 6 PS10 back today; PS11 due today. PS12 due Monday December 13. 1. The genus of a nonsingular projective curve The definition I’m going to give you isn’t the one people would typically start with. I prefer to introduce this one here, because it is more easily computable. Definition. The tentative genus of a nonsingular projective curve C is given by 1 − deg ΩC =2g 2. Fact (from Riemann-Roch, later). g is always a nonnegative integer, i.e. deg K = −2, 0, 2,.... Complex picture: Riemann-surface with g “holes”. Examples. Hence P1 has genus 0, smooth plane cubics have genus 1, etc. Exercise: Hyperelliptic curves. Suppose f(x0,x1) is a polynomial of homo- geneous degree n where n is even. Let C0 be the affine plane curve given by 2 y = f(1,x1), with the generically 2-to-1 cover C0 → U0.LetC1be the affine 2 plane curve given by z = f(x0, 1), with the generically 2-to-1 cover C1 → U1. Check that C0 and C1 are nonsingular. Show that you can glue together C0 and C1 (and the double covers) so as to give a double cover C → P1. (For computational convenience, you may assume that neither [0; 1] nor [1; 0] are zeros of f.) What goes wrong if n is odd? Show that the tentative genus of C is n/2 − 1.(Thisisa special case of the Riemann-Hurwitz formula.) This provides examples of curves of any genus. -
CHAPTER 0 PRELIMINARY MATERIAL Paul
CHAPTER 0 PRELIMINARY MATERIAL Paul Vojta University of California, Berkeley 18 February 1998 This chapter gives some preliminary material on number theory and algebraic geometry. Section 1 gives basic preliminary notation, both mathematical and logistical. Sec- tion 2 describes what algebraic geometry is assumed of the reader, and gives a few conventions that will be assumed here. Section 3 gives a few more details on the field of definition of a variety. Section 4 does the same as Section 2 for number theory. The remaining sections of this chapter give slightly longer descriptions of some topics in algebraic geometry that will be needed: Kodaira’s lemma in Section 5, and descent in Section 6. x1. General notation The symbols Z , Q , R , and C stand for the ring of rational integers and the fields of rational numbers, real numbers, and complex numbers, respectively. The symbol N sig- nifies the natural numbers, which in this book start at zero: N = f0; 1; 2; 3;::: g . When it is necessary to refer to the positive integers, we use subscripts: Z>0 = f1; 2; 3;::: g . Similarly, R stands for the set of nonnegative real numbers, etc. ¸0 ` ` The set of extended real numbers is the set R := f¡1g R f1g . It carries the obvious ordering. ¯ ¯ If k is a field, then k denotes an algebraic closure of k . If ® 2 k , then Irr®;k(X) is the (unique) monic irreducible polynomial f 2 k[X] for which f(®) = 0 . Unless otherwise specified, the wording almost all will mean all but finitely many. -
Algebraic Geometry Michael Stoll
Introductory Geometry Course No. 100 351 Fall 2005 Second Part: Algebraic Geometry Michael Stoll Contents 1. What Is Algebraic Geometry? 2 2. Affine Spaces and Algebraic Sets 3 3. Projective Spaces and Algebraic Sets 6 4. Projective Closure and Affine Patches 9 5. Morphisms and Rational Maps 11 6. Curves — Local Properties 14 7. B´ezout’sTheorem 18 2 1. What Is Algebraic Geometry? Linear Algebra can be seen (in parts at least) as the study of systems of linear equations. In geometric terms, this can be interpreted as the study of linear (or affine) subspaces of Cn (say). Algebraic Geometry generalizes this in a natural way be looking at systems of polynomial equations. Their geometric realizations (their solution sets in Cn, say) are called algebraic varieties. Many questions one can study in various parts of mathematics lead in a natural way to (systems of) polynomial equations, to which the methods of Algebraic Geometry can be applied. Algebraic Geometry provides a translation between algebra (solutions of equations) and geometry (points on algebraic varieties). The methods are mostly algebraic, but the geometry provides the intuition. Compared to Differential Geometry, in Algebraic Geometry we consider a rather restricted class of “manifolds” — those given by polynomial equations (we can allow “singularities”, however). For example, y = cos x defines a perfectly nice differentiable curve in the plane, but not an algebraic curve. In return, we can get stronger results, for example a criterion for the existence of solutions (in the complex numbers), or statements on the number of solutions (for example when intersecting two curves), or classification results. -
Trigonometry Cram Sheet
Trigonometry Cram Sheet August 3, 2016 Contents 6.2 Identities . 8 1 Definition 2 7 Relationships Between Sides and Angles 9 1.1 Extensions to Angles > 90◦ . 2 7.1 Law of Sines . 9 1.2 The Unit Circle . 2 7.2 Law of Cosines . 9 1.3 Degrees and Radians . 2 7.3 Law of Tangents . 9 1.4 Signs and Variations . 2 7.4 Law of Cotangents . 9 7.5 Mollweide’s Formula . 9 2 Properties and General Forms 3 7.6 Stewart’s Theorem . 9 2.1 Properties . 3 7.7 Angles in Terms of Sides . 9 2.1.1 sin x ................... 3 2.1.2 cos x ................... 3 8 Solving Triangles 10 2.1.3 tan x ................... 3 8.1 AAS/ASA Triangle . 10 2.1.4 csc x ................... 3 8.2 SAS Triangle . 10 2.1.5 sec x ................... 3 8.3 SSS Triangle . 10 2.1.6 cot x ................... 3 8.4 SSA Triangle . 11 2.2 General Forms of Trigonometric Functions . 3 8.5 Right Triangle . 11 3 Identities 4 9 Polar Coordinates 11 3.1 Basic Identities . 4 9.1 Properties . 11 3.2 Sum and Difference . 4 9.2 Coordinate Transformation . 11 3.3 Double Angle . 4 3.4 Half Angle . 4 10 Special Polar Graphs 11 3.5 Multiple Angle . 4 10.1 Limaçon of Pascal . 12 3.6 Power Reduction . 5 10.2 Rose . 13 3.7 Product to Sum . 5 10.3 Spiral of Archimedes . 13 3.8 Sum to Product . 5 10.4 Lemniscate of Bernoulli . 13 3.9 Linear Combinations . -
Study of Spiral Transition Curves As Related to the Visual Quality of Highway Alignment
A STUDY OF SPIRAL TRANSITION CURVES AS RELA'^^ED TO THE VISUAL QUALITY OF HIGHWAY ALIGNMENT JERRY SHELDON MURPHY B, S., Kansas State University, 1968 A MJvSTER'S THESIS submitted in partial fulfillment of the requirements for the degree MASTER OF SCIENCE Department of Civil Engineering KANSAS STATE UNIVERSITY Manhattan, Kansas 1969 Approved by P^ajQT Professor TV- / / ^ / TABLE OF CONTENTS <2, 2^ INTRODUCTION 1 LITERATURE SEARCH 3 PURPOSE 5 SCOPE 6 • METHOD OF SOLUTION 7 RESULTS 18 RECOMMENDATIONS FOR FURTHER RESEARCH 27 CONCLUSION 33 REFERENCES 34 APPENDIX 36 LIST OF TABLES TABLE 1, Geonetry of Locations Studied 17 TABLE 2, Rates of Change of Slope Versus Curve Ratings 31 LIST OF FIGURES FIGURE 1. Definition of Sight Distance and Display Angle 8 FIGURE 2. Perspective Coordinate Transformation 9 FIGURE 3. Spiral Curve Calculation Equations 12 FIGURE 4. Flow Chart 14 FIGURE 5, Photograph and Perspective of Selected Location 15 FIGURE 6. Effect of Spiral Curves at Small Display Angles 19 A, No Spiral (Circular Curve) B, Completely Spiralized FIGURE 7. Effects of Spiral Curves (DA = .015 Radians, SD = 1000 Feet, D = l** and A = 10*) 20 Plate 1 A. No Spiral (Circular Curve) B, Spiral Length = 250 Feet FIGURE 8. Effects of Spiral Curves (DA = ,015 Radians, SD = 1000 Feet, D = 1° and A = 10°) 21 Plate 2 A. Spiral Length = 500 Feet B. Spiral Length = 1000 Feet (Conpletely Spiralized) FIGURE 9. Effects of Display Angle (D = 2°, A = 10°, Ig = 500 feet, = SD 500 feet) 23 Plate 1 A. Display Angle = .007 Radian B. Display Angle = .027 Radiaji FIGURE 10. -
1 Affine Varieties
1 Affine Varieties We will begin following Kempf's Algebraic Varieties, and eventually will do things more like in Hartshorne. We will also use various sources for commutative algebra. What is algebraic geometry? Classically, it is the study of the zero sets of polynomials. We will now fix some notation. k will be some fixed algebraically closed field, any ring is commutative with identity, ring homomorphisms preserve identity, and a k-algebra is a ring R which contains k (i.e., we have a ring homomorphism ι : k ! R). P ⊆ R an ideal is prime iff R=P is an integral domain. Algebraic Sets n n We define affine n-space, A = k = f(a1; : : : ; an): ai 2 kg. n Any f = f(x1; : : : ; xn) 2 k[x1; : : : ; xn] defines a function f : A ! k : (a1; : : : ; an) 7! f(a1; : : : ; an). Exercise If f; g 2 k[x1; : : : ; xn] define the same function then f = g as polynomials. Definition 1.1 (Algebraic Sets). Let S ⊆ k[x1; : : : ; xn] be any subset. Then V (S) = fa 2 An : f(a) = 0 for all f 2 Sg. A subset of An is called algebraic if it is of this form. e.g., a point f(a1; : : : ; an)g = V (x1 − a1; : : : ; xn − an). Exercises 1. I = (S) is the ideal generated by S. Then V (S) = V (I). 2. I ⊆ J ) V (J) ⊆ V (I). P 3. V ([αIα) = V ( Iα) = \V (Iα). 4. V (I \ J) = V (I · J) = V (I) [ V (J). Definition 1.2 (Zariski Topology). We can define a topology on An by defining the closed subsets to be the algebraic subsets. -
ON the FIELD of DEFINITION of P-TORSION POINTS on ELLIPTIC CURVES OVER the RATIONALS
ON THE FIELD OF DEFINITION OF p-TORSION POINTS ON ELLIPTIC CURVES OVER THE RATIONALS ALVARO´ LOZANO-ROBLEDO Abstract. Let SQ(d) be the set of primes p for which there exists a number field K of degree ≤ d and an elliptic curve E=Q, such that the order of the torsion subgroup of E(K) is divisible by p. In this article we give bounds for the primes in the set SQ(d). In particular, we show that, if p ≥ 11, p 6= 13; 37, and p 2 SQ(d), then p ≤ 2d + 1. Moreover, we determine SQ(d) for all d ≤ 42, and give a conjectural formula for all d ≥ 1. If Serre’s uniformity problem is answered positively, then our conjectural formula is valid for all sufficiently large d. Under further assumptions on the non-cuspidal points on modular curves that parametrize those j-invariants associated to Cartan subgroups, the formula is valid for all d ≥ 1. 1. Introduction Let K be a number field of degree d ≥ 1 and let E=K be an elliptic curve. The Mordell-Weil theorem states that E(K), the set of K-rational points on E, can be given the structure of a finitely ∼ R generated abelian group. Thus, there is an integer R ≥ 0 such that E(K) = E(K)tors ⊕ Z and the torsion subgroup E(K)tors is finite. Here, we will focus on the order of E(K)tors. In particular, we are interested in the following question: if we fix d ≥ 1, what are the possible prime divisors of the order of E(K)tors, for E and K as above? Definition 1.1. -
RATIONAL HOMOGENEOUS VARIETIES Giorgio Ottaviani
RATIONAL HOMOGENEOUS VARIETIES Giorgio Ottaviani Dipartimento di Matematica, Universit`adell'Aquila Current address: Dipartimento di Matematica, Universit`adi Firenze viale Morgagni 67/A 50134 FIRENZE [email protected]fi.it x1. Introduction page 1 x2. Grassmannians and flag varieties 5 x3. Lie algebras and Lie groups 9 x4. The Borel fixed point theorem 18 x5. SL(2) 22 x6. The Cartan decomposition 26 x7. Borel and parabolic subgroups 37 x8. ABC about bundles 40 x9. Homogeneous bundles 47 x10. The theorem of Borel-Weil 51 x11. The theorem of Bott 61 x12. Stability of homogeneous bundles 65 References 69 These notes have been written for distribution to the participants to the summer school in Algebraic Geometry organized by the Scuola Matematica Universitaria in Cortona in the period 13-26 August 1995. The aim was to describe the classification of rational homogeneous varieties and to provide the theorems of Borel-Weil and Bott. Lie algebras are introduced starting from the definition and they are studied as far as it is necessary for the aim. At the other side, the knowledge of basic techniques of algebraic geometry (as sheaf cohomology) and algebraic topology was assumed. I learned most of the material of these notes from many lectures and discussions with Vincenzo Ancona and Alan Huckleberry. I am sincerely grateful to both of them and also to all the participants to the course in Cortona, especially to Raffaella Paoletti and Anke Simon for careful proofreading and for their suggestions. x1. Introduction An algebraic variety is a quasiprojective variety over the field C of complex numbers. -
Graduate Texts in Mathematics
Graduate Texts in Mathematics Editorial Board S. Axler F.W. Gehring K.A. Ribet BOOKS OF RELATED INTEREST BY SERGE LANG Math Talks for Undergraduates 1999, ISBN 0-387-98749-5 Linear Algebra, Third Edition 1987, ISBN 0-387-96412-6 Undergraduate Algebra, Second Edition 1990, ISBN 0-387-97279-X Undergraduate Analysis, Second Edition 1997, ISBN 0-387-94841-4 Complex Analysis, Third Edition 1993, ISBN 0-387-97886 Real and Functional Analysis, Third Edition 1993, ISBN 0-387-94001-4 Algebraic Number Theory, Second Edition 1994, ISBN 0-387-94225-4 OTHER BOOKS BY LANG PUBLISHED BY SPRINGER-VERLAG Introduction to Arakelov Theory • Riemann-Roch Algebra (with William Fulton) • Complex Multiplication • Introduction to Modular Forms • Modular Units (with Daniel Kubert) • Fundamentals of Diophantine Geometry • Elliptic Functions • Number Theory III • Survey of Diophantine Geometry • Fundamentals of Differential Geometry • Cyclotomic Fields I and II • SL2(R) • Abelian Varieties • Introduction to Algebraic and Abelian Functions • Introduction to Diophantine Approximations • Elliptic Curves: Diophantine Analysis • Introduction to Linear Algebra • Calculus of Several Variables • First Course in Calculus • Basic Mathematics • Geometry: A High School Course (with Gene Murrow) • Math! Encounters with High School Students • The Beauty of Doing Mathematics • THE FILE • CHALLENGES Serge Lang Algebra Revised Third Edition Springer Serge Lang Department of Mathematics Yale University New Haven, CT 96520 USA Editorial Board S. Axler Mathematics Department F.W. Gehring K.A. Ribet San Francisco State Mathematics Department Mathematics Department University East Hall University of California, San Francisco, CA 94132 University of Michigan Berkeley USA Ann Arbor, MI 48109 Berkeley, CA 94720-3840 [email protected] USA USA [email protected]. -
THE GALOIS ACTION on DESSIN D'enfants Contents 1. Introduction 1 2. Background: the Absolute Galois Group 4 3. Background
THE GALOIS ACTION ON DESSIN D'ENFANTS CARSON COLLINS Abstract. We introduce the theory of dessin d'enfants, with emphasis on how it relates to the absolute Galois group of Q. We prove Belyi's Theorem and show how the resulting Galois action is faithful on dessins. We also discuss the action on categories equivalent to dessins and prove its most powerful invariants for classifying orbits of the action. Minimal background in Galois theory or algebraic geometry is assumed, and we review those concepts which are necessary to this task. Contents 1. Introduction 1 2. Background: The Absolute Galois Group 4 3. Background: Algebraic Curves 4 4. Belyi's Theorem 5 5. The Galois Action on Dessins 6 6. Computing the Belyi Map of a Spherical Dessin 7 7. Faithfulness of the Galois Action 9 8. Cartographic and Automorphism Groups of a Dessin 10 9. Regular Dessins: A Galois Correspondence 13 Acknowledgments 16 References 16 1. Introduction Definition 1.1. A bigraph is a connected bipartite graph with a fixed 2-coloring into nonempty sets of black and white vertices. We refer to the edges of a bigraph as its darts. Definition 1.2. A dessin is a bigraph with an embedding into a topological surface such that its complement in the surface is a disjoint union of open disks, called the faces of the dessin. Dessin d'enfant, often abbreviated to dessin, is French for "child's drawing." As the definition above demonstrates, these are simple combinatorial objects, yet they have subtle and deep connections to algebraic geometry and Galois theory.