Hyperelliptic Curves with Many Automorphisms
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21 the Hilbert Class Polynomial
18.783 Elliptic Curves Spring 2015 Lecture #21 04/28/2015 21 The Hilbert class polynomial In the previous lecture we proved that the field of modular functions for Γ0(N) is generated by the functions j(τ) and jN (τ) := j(Nτ), and we showed that C(j; jN ) is a finite extension of C(j). We then defined the classical modular polynomial ΦN (Y ) as the minimal polynomial of jN over C(j), and we proved that its coefficients are integer polynomials in j. Replacing j with a new variable X, we can view ΦN Z[X; Y ] as an integer polynomial in two variables. In this lecture we will use ΦN to prove that the Hilbert class polynomial Y HD(X) := (X − j(E)) j(E)2EllO(C) also has integer coefficients; here D = disc(O) and EllO(C) := fj(E) : End(E) ' Og is the finite set of j-invariants of elliptic curves E=C with complex multiplication (CM) by O. This implies that each j(E) 2 EllO(C) is an algebraic integer, meaning that any elliptic curve E=C with complex multiplication can actually be defined over a finite extension of Q (a number field). This fact is the key to relating the theory of elliptic curves over the complex numbers to elliptic curves over finite fields. 21.1 Isogenies Recall from Lecture 18 that if L1 is a sublattice of L2, and E1 ' C=L1 and E2 ' C=L2 are the corresponding elliptic curves, then there is an isogeny φ: E1 ! E2 whose kernel is isomorphic to the finite abelian group L2=L1. -
Abelian Varieties with Complex Multiplication and Modular Functions, by Goro Shimura, Princeton Univ
BULLETIN (New Series) OF THE AMERICAN MATHEMATICAL SOCIETY Volume 36, Number 3, Pages 405{408 S 0273-0979(99)00784-3 Article electronically published on April 27, 1999 Abelian varieties with complex multiplication and modular functions, by Goro Shimura, Princeton Univ. Press, Princeton, NJ, 1998, xiv + 217 pp., $55.00, ISBN 0-691-01656-9 The subject that might be called “explicit class field theory” begins with Kro- necker’s Theorem: every abelian extension of the field of rational numbers Q is a subfield of a cyclotomic field Q(ζn), where ζn is a primitive nth root of 1. In other words, we get all abelian extensions of Q by adjoining all “special values” of e(x)=exp(2πix), i.e., with x Q. Hilbert’s twelfth problem, also called Kronecker’s Jugendtraum, is to do something2 similar for any number field K, i.e., to generate all abelian extensions of K by adjoining special values of suitable special functions. Nowadays we would add that the reciprocity law describing the Galois group of an abelian extension L/K in terms of ideals of K should also be given explicitly. After K = Q, the next case is that of an imaginary quadratic number field K, with the real torus R/Z replaced by an elliptic curve E with complex multiplication. (Kronecker knew what the result should be, although complete proofs were given only later, by Weber and Takagi.) For simplicity, let be the ring of integers in O K, and let A be an -ideal. Regarding A as a lattice in C, we get an elliptic curve O E = C/A with End(E)= ;Ehas complex multiplication, or CM,by .If j=j(A)isthej-invariant ofOE,thenK(j) is the Hilbert class field of K, i.e.,O the maximal abelian unramified extension of K. -
Chapter 5 Complex Numbers
Chapter 5 Complex numbers Why be one-dimensional when you can be two-dimensional? ? 3 2 1 0 1 2 3 − − − ? We begin by returning to the familiar number line, where I have placed the question marks there appear to be no numbers. I shall rectify this by defining the complex numbers which give us a number plane rather than just a number line. Complex numbers play a fundamental rˆolein mathematics. In this chapter, I shall use them to show how e and π are connected and how certain primes can be factorized. They are also fundamental to physics where they are used in quantum mechanics. 5.1 Complex number arithmetic In the set of real numbers we can add, subtract, multiply and divide, but we cannot always extract square roots. For example, the real number 1 has 125 126 CHAPTER 5. COMPLEX NUMBERS the two real square roots 1 and 1, whereas the real number 1 has no real square roots, the reason being that− the square of any real non-zero− number is always positive. In this section, we shall repair this lack of square roots and, as we shall learn, we shall in fact have achieved much more than this. Com- plex numbers were first studied in the 1500’s but were only fully accepted and used in the 1800’s. Warning! If r is a positive real number then √r is usually interpreted to mean the positive square root. If I want to emphasize that both square roots need to be considered I shall write √r. -
Diophantine Problems in Polynomial Theory
Diophantine Problems in Polynomial Theory by Paul David Lee B.Sc. Mathematics, The University of British Columbia, 2009 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in The College of Graduate Studies (Mathematics) THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan) August 2011 c Paul David Lee 2011 Abstract Algebraic curves and surfaces are playing an increasing role in mod- ern mathematics. From the well known applications to cryptography, to computer vision and manufacturing, studying these curves is a prevalent problem that is appearing more often. With the advancement of computers, dramatic progress has been made in all branches of algebraic computation. In particular, computer algebra software has made it much easier to find rational or integral points on algebraic curves. Computers have also made it easier to obtain rational parametrizations of certain curves and surfaces. Each algebraic curve has an associated genus, essentially a classification, that determines its topological structure. Advancements on methods and theory on curves of genus 0, 1 and 2 have been made in recent years. Curves of genus 0 are the only algebraic curves that you can obtain a rational parametrization for. Curves of genus 1 (also known as elliptic curves) have the property that their rational points have a group structure and thus one can call upon the massive field of group theory to help with their study. Curves of higher genus (such as genus 2) do not have the background and theory that genus 0 and 1 do but recent advancements in theory have rapidly expanded advancements on the topic. -
GEOMETRY and NUMBERS Ching-Li Chai
GEOMETRY AND NUMBERS Ching-Li Chai Sample arithmetic statements Diophantine equations Counting solutions of a GEOMETRY AND NUMBERS diophantine equation Counting congruence solutions L-functions and distribution of prime numbers Ching-Li Chai Zeta and L-values Sample of geometric structures and symmetries Institute of Mathematics Elliptic curve basics Academia Sinica Modular forms, modular and curves and Hecke symmetry Complex multiplication Department of Mathematics Frobenius symmetry University of Pennsylvania Monodromy Fine structure in characteristic p National Chiao Tung University, July 6, 2012 GEOMETRY AND Outline NUMBERS Ching-Li Chai Sample arithmetic 1 Sample arithmetic statements statements Diophantine equations Diophantine equations Counting solutions of a diophantine equation Counting solutions of a diophantine equation Counting congruence solutions L-functions and distribution of Counting congruence solutions prime numbers L-functions and distribution of prime numbers Zeta and L-values Sample of geometric Zeta and L-values structures and symmetries Elliptic curve basics Modular forms, modular 2 Sample of geometric structures and symmetries curves and Hecke symmetry Complex multiplication Elliptic curve basics Frobenius symmetry Monodromy Modular forms, modular curves and Hecke symmetry Fine structure in characteristic p Complex multiplication Frobenius symmetry Monodromy Fine structure in characteristic p GEOMETRY AND The general theme NUMBERS Ching-Li Chai Sample arithmetic statements Diophantine equations Counting solutions of a Geometry and symmetry influences diophantine equation Counting congruence solutions L-functions and distribution of arithmetic through zeta functions and prime numbers Zeta and L-values modular forms Sample of geometric structures and symmetries Elliptic curve basics Modular forms, modular Remark. (i) zeta functions = L-functions; curves and Hecke symmetry Complex multiplication modular forms = automorphic representations. -
Determining the Automorphism Group of a Hyperelliptic Curve
Determining the Automorphism Group of a Hyperelliptic Curve ∗ Tanush Shaska Department of Mathematics University of California at Irvine 103 MSTB, Irvine, CA 92697 ABSTRACT 1. INTRODUCTION In this note we discuss techniques for determining the auto- Let Xg be an algebraic curve of genus g defined over an morphism group of a genus g hyperelliptic curve Xg defined algebraically closed field k of characteristic zero. We denote over an algebraically closed field k of characteristic zero. by Aut(Xg) the group of analytic (equivalently, algebraic) The first technique uses the classical GL2(k)-invariants of automorphisms of Xg. Then Aut(Xg) acts on the finite set binary forms. This is a practical method for curves of small of Weierstrass points of Xg. This action is faithful unless genus, but has limitations as the genus increases, due to the Xg is hyperelliptic, in which case its kernel is the group of fact that such invariants are not known for large genus. order 2 containing the hyperelliptic involution of Xg. Thus The second approach, which uses dihedral invariants of in any case, Aut(Xg) is a finite group. This was first proved hyperelliptic curves, is a very convenient method and works by Schwartz. In 1893 Hurwitz discovered what is now called well in all genera. First we define the normal decomposition the Riemann-Hurwitz formula. From this he derived that of a hyperelliptic curve with extra automorphisms. Then dihedral invariants are defined in terms of the coefficients of |Aut(Xg)| ≤ 84 (g − 1) this normal decomposition. We define such invariants inde- which is known as the Hurwitz bound. -
Geometry of Algebraic Curves
Geometry of Algebraic Curves Fall 2011 Course taught by Joe Harris Notes by Atanas Atanasov One Oxford Street, Cambridge, MA 02138 E-mail address: [email protected] Contents Lecture 1. September 2, 2011 6 Lecture 2. September 7, 2011 10 2.1. Riemann surfaces associated to a polynomial 10 2.2. The degree of KX and Riemann-Hurwitz 13 2.3. Maps into projective space 15 2.4. An amusing fact 16 Lecture 3. September 9, 2011 17 3.1. Embedding Riemann surfaces in projective space 17 3.2. Geometric Riemann-Roch 17 3.3. Adjunction 18 Lecture 4. September 12, 2011 21 4.1. A change of viewpoint 21 4.2. The Brill-Noether problem 21 Lecture 5. September 16, 2011 25 5.1. Remark on a homework problem 25 5.2. Abel's Theorem 25 5.3. Examples and applications 27 Lecture 6. September 21, 2011 30 6.1. The canonical divisor on a smooth plane curve 30 6.2. More general divisors on smooth plane curves 31 6.3. The canonical divisor on a nodal plane curve 32 6.4. More general divisors on nodal plane curves 33 Lecture 7. September 23, 2011 35 7.1. More on divisors 35 7.2. Riemann-Roch, finally 36 7.3. Fun applications 37 7.4. Sheaf cohomology 37 Lecture 8. September 28, 2011 40 8.1. Examples of low genus 40 8.2. Hyperelliptic curves 40 8.3. Low genus examples 42 Lecture 9. September 30, 2011 44 9.1. Automorphisms of genus 0 an 1 curves 44 9.2. -
Symmetry Types of Hyperelliptic Riemann Surfaces
MEMOIRES´ DE LA SMF 86 SYMMETRY TYPES OF HYPERELLIPTIC RIEMANN SURFACES Emilio Bujalance Francisco-Javier Cirre J.-M. Gamboa Grzegorz Gromadzki Soci´et´eMath´ematique de France 2001 Publi´eavecleconcoursduCentreNationaldelaRechercheScientifique 2000 Mathematics Subject Classification.— Key words and phrases.— Abstract.— X τ : X X → Aut±X X g ! 2 Résumé (Types de symétrie des surfaces de Riemann hyperelliptiques) X τ : X X → Aut±X X g ! 2 ! CONTENTS Introduction................................................................... 1 1. Preliminaries............................................................... 7 1.1. Klein surfaces and NEC groups.. 7 1.2. Symmetric Riemann surfaces. 13 1.3. Hyperelliptic real algebraic curves........................................ 15 2. Automorphism groups of symmetric hyperelliptic Riemann surfaces.. 21 2.1. On signatures of the automorphism groups.. 21 2.2. Number of real forms. 26 2.3. Automorphism groups of symmetric hyperelliptic Riemann surfaces. 43 3. Symmetry types of hyperelliptic Riemann surfaces.................... 49 3.1. Symmetry types of hyperelliptic algebraic curves of class I. 50 3.2. Symmetry types of hyperelliptic algebraic curves of class II. ............. 65 3.3. Symmetry types of hyperelliptic algebraic curves of class III. ........... 72 3.4. Symmetry types of hyperelliptic algebraic curves of class IV. ............. 79 3.5. Symmetry types of hyperelliptic algebraic curves of class V. ............. 92 3.6. Symmetry types of hyperelliptic algebraic curves of class VI. ............. 97 3.7. Symmetry types of hyperelliptic algebraic curves of class VII. ............102 3.8. Symmetry types of hyperelliptic algebraic curves of class VIII............109 3.9. Symmetry types of hyperelliptic algebraic curves of class IX. .............115 3.10. Symmetry types of hyperelliptic algebraic curves of class X. ..........117 Bibliography...................................................................119 INTRODUCTION Let X be a compact Riemann surface. -
Log Minimal Model Program for the Moduli Space of Stable Curves: the Second Flip
LOG MINIMAL MODEL PROGRAM FOR THE MODULI SPACE OF STABLE CURVES: THE SECOND FLIP JAROD ALPER, MAKSYM FEDORCHUK, DAVID ISHII SMYTH, AND FREDERICK VAN DER WYCK Abstract. We prove an existence theorem for good moduli spaces, and use it to construct the second flip in the log minimal model program for M g. In fact, our methods give a uniform self-contained construction of the first three steps of the log minimal model program for M g and M g;n. Contents 1. Introduction 2 Outline of the paper 4 Acknowledgments 5 2. α-stability 6 2.1. Definition of α-stability6 2.2. Deformation openness 10 2.3. Properties of α-stability 16 2.4. αc-closed curves 18 2.5. Combinatorial type of an αc-closed curve 22 3. Local description of the flips 27 3.1. Local quotient presentations 27 3.2. Preliminary facts about local VGIT 30 3.3. Deformation theory of αc-closed curves 32 3.4. Local VGIT chambers for an αc-closed curve 40 4. Existence of good moduli spaces 45 4.1. General existence results 45 4.2. Application to Mg;n(α) 54 5. Projectivity of the good moduli spaces 64 5.1. Main positivity result 67 5.2. Degenerations and simultaneous normalization 69 5.3. Preliminary positivity results 74 5.4. Proof of Theorem 5.5(a) 79 5.5. Proof of Theorem 5.5(b) 80 Appendix A. 89 References 92 1 2 ALPER, FEDORCHUK, SMYTH, AND VAN DER WYCK 1. Introduction In an effort to understand the canonical model of M g, Hassett and Keel introduced the log minimal model program (LMMP) for M . -
Lesson 3: Roots of Unity
NYS COMMON CORE MATHEMATICS CURRICULUM Lesson 3 M3 PRECALCULUS AND ADVANCED TOPICS Lesson 3: Roots of Unity Student Outcomes . Students determine the complex roots of polynomial equations of the form 푥푛 = 1 and, more generally, equations of the form 푥푛 = 푘 positive integers 푛 and positive real numbers 푘. Students plot the 푛th roots of unity in the complex plane. Lesson Notes This lesson ties together work from Algebra II Module 1, where students studied the nature of the roots of polynomial equations and worked with polynomial identities and their recent work with the polar form of a complex number to find the 푛th roots of a complex number in Precalculus Module 1 Lessons 18 and 19. The goal here is to connect work within the algebra strand of solving polynomial equations to the geometry and arithmetic of complex numbers in the complex plane. Students determine solutions to polynomial equations using various methods and interpreting the results in the real and complex plane. Students need to extend factoring to the complex numbers (N-CN.C.8) and more fully understand the conclusion of the fundamental theorem of algebra (N-CN.C.9) by seeing that a polynomial of degree 푛 has 푛 complex roots when they consider the roots of unity graphed in the complex plane. This lesson helps students cement the claim of the fundamental theorem of algebra that the equation 푥푛 = 1 should have 푛 solutions as students find all 푛 solutions of the equation, not just the obvious solution 푥 = 1. Students plot the solutions in the plane and discover their symmetry. -
The Twelfth Problem of Hilbert Reminds Us, Although the Reminder Should
Some Contemporary Problems with Origins in the Jugendtraum Robert P. Langlands The twelfth problem of Hilbert reminds us, although the reminder should be unnecessary, of the blood relationship of three subjects which have since undergone often separate devel• opments. The first of these, the theory of class fields or of abelian extensions of number fields, attained what was pretty much its final form early in this century. The second, the algebraic theory of elliptic curves and, more generally, of abelian varieties, has been for fifty years a topic of research whose vigor and quality shows as yet no sign of abatement. The third, the theory of automorphic functions, has been slower to mature and is still inextricably entangled with the study of abelian varieties, especially of their moduli. Of course at the time of Hilbert these subjects had only begun to set themselves off from the general mathematical landscape as separate theories and at the time of Kronecker existed only as part of the theories of elliptic modular functions and of cyclotomicfields. It is in a letter from Kronecker to Dedekind of 1880,1 in which he explains his work on the relation between abelian extensions of imaginary quadratic fields and elliptic curves with complex multiplication, that the word Jugendtraum appears. Because these subjects were so interwoven it seems to have been impossible to disentangle the different kinds of mathematics which were involved in the Jugendtraum, especially to separate the algebraic aspects from the analytic or number theoretic. Hilbert in particular may have been led to mistake an accident, or perhaps necessity, of historical development for an “innigste gegenseitige Ber¨uhrung.” We may be able to judge this better if we attempt to view the mathematical content of the Jugendtraum with the eyes of a sophisticated contemporary mathematician. -
Ordinary Plane Models and Completely Split Divisors
Ordinary plane models and completely split divisors Claus Diem and Sebastian Kochinke March 21, 2019 Abstract Let C be a smooth, non-hyperelliptic curve over an algebraically closed field of genus g ≥ 4. We show that the projection from the canonical model of C through (g −3) generic points on C is a birational morphism to a plane curve which has only finitely many non-ordinary tangents, that is, flex- or bitangents. For smooth, non-hyperelliptic curves of a fixed genus g ≥ 4 over finite fields, we show that the proba- bility that an effective divisor of degree (g−3) defines such an \ordinary (birational) plane model" converges to 1. This result has an application to the solution of the discrete loga- rithm problem for smooth, non-hyperelliptic curves curves of a fixed genus g over finite fields Fq: By first changing the representation to such an ordinary plane model and then using an algorithm by the first 2 ~ 2− g−1 author, the problem can be solved in an expected time of O(q ). Another consequence is that for smooth, non-hyperelliptic curves of a fixed genus g over finite fields Fq, the number of completely split 1 q−1 divisors in the canonical system is ∼ (2g+2)! ⋅ q . 1 Introduction Let us consider the discrete logarithm problem in the degree-0 Picard groups of smooth curves of a fixed genus g. In [Die11] it is shown that this problem can be solved in an expected time of 2− 2 ~ g Oq ; here and in the following the phrase \expected time" refers to an internal randomization of the algorithm.