Patching and Galois Theory David Harbater∗ Dept. of Mathematics
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Inverse Galois Problem with Viewpoint to Galois Theory and It's Applications
Vol-3 Issue-4 2017 IJARIIE-ISSN(O)-2395-4396 INVERSE GALOIS PROBLEM WITH VIEWPOINT TO GALOIS THEORY AND IT’S APPLICATIONS Dr. Ajay Kumar Gupta1, Vinod Kumar2 1 Associate Professor, Bhagwant Institute of Technology, Muzaffarnagar,Uttar Pradesh, India 2 Research Scholar, Deptt. Of Mathematics, Bhagwant University, Ajmer, Rajasthan, India ABSTRACT In this paper we are presenting a review of the inverse Galois Problem and its applications. In mathematics, more specifically in abstract algebra, Galois Theory, named after Évariste Galois, provides a connection between field theory and group theory. Using Galois Theory, certain problems in field theory can be reduced to group theory, which is, in some sense, simpler and better understood. Originally, Galois used permutation groups to describe how the various roots of a given polynomial equation are related to each other. Galois Theory is the algebraic study of groups that can be associated with polynomial equations. In this survey we outline the milestones of the Inverse Problem of Galois theory historically up to the present time. We summarize as well the contribution of the authors to the Galois Embedding Problem, which is the most natural approach to the Inverse Problem in the case of non-simple groups. Keyword : - Problem, Contribution, Field Theory, and Simple Group etc. 1. INTRODUCTION The inverse problem of Galois Theory was developed in the early 1800’s as an approach to understand polynomials and their roots. The inverse Galois problem states whether any finite group can be realized as a Galois group over ℚ (field of rational numbers). There has been considerable progress in this as yet unsolved problem. -
QUALIFYING EXAMINATION Harvard University Department of Mathematics Tuesday, October 24, 1995 (Day 1)
QUALIFYING EXAMINATION Harvard University Department of Mathematics Tuesday, October 24, 1995 (Day 1) 1. Let K be a ¯eld of characteristic 0. a. Find three nonconstant polynomials x(t); y(t); z(t) K[t] such that 2 x2 + y2 = z2 b. Now let n be any integer, n 3. Show that there do not exist three nonconstant polynomials x(t); y(t); z(t) K[t] suc¸h that 2 xn + yn = zn: 2. For any integers k and n with 1 k n, let · · Sn = (x ; : : : ; x ) : x2 + : : : + x2 = 1 n+1 f 1 n+1 1 n+1 g ½ be the n-sphere, and let D n+1 be the closed disc k ½ D = (x ; : : : ; x ) : x2 + : : : + x2 1; x = : : : = x = 0 n+1: k f 1 n+1 1 k · k+1 n+1 g ½ n Let X = S D be their union. Calculate the cohomology ring H¤(X ; ¡ ). k;n [ k k;n 2 3. Let f : be any 1 map such that ! C @2f @2f + 0: @x2 @y2 ´ Show that if f is not surjective then it is constant. 4. Let G be a ¯nite group, and let ; ¿ G be two elements selected at random from G (with the uniform distribution). In terms2 of the order of G and the number of conjugacy classes of G, what is the probability that and ¿ commute? What is the probability if G is the symmetric group S5 on 5 letters? 1 5. Let be the region given by ½ = z : z 1 < 1 and z i < 1 : f j ¡ j j ¡ j g Find a conformal map f : ¢ of onto the unit disc ¢ = z : z < 1 . -
THE INVERSE GALOIS PROBLEM OVER C(Z)
THE INVERSE GALOIS PROBLEM OVER C(z) ARNO FEHM, DAN HARAN AND ELAD PARAN Abstract. We give a self-contained elementary solution for the inverse Galois problem over the field of rational functions over the complex numbers. 1. Introduction Since the 19th century one of the foundational open questions of Galois theory is the inverse Galois problem, which asks whether every finite group occurs as the Galois group of a Galois extension of the field Q of rational numbers. In 1892 Hilbert proved his cele- brated irreducibility theorem and deduced that the inverse Galois problem has a positive answer provided that every finite group occurs as the Galois group of a Galois extension of the field Q(z) of rational functions over Q. It was known already back then that the analogous problem for the field C(z) of rational functions over the complex numbers indeed has a positive answer: Every finite group occurs as the Galois group of a Galois extension of C(z). The aim of this work is to give a new and elementary proof of this result which uses only basic complex analysis and field theory. The value of such a proof becomes clear when compared to the previously known ones: 1.1. Classical proof using Riemann's existence theorem. The classical proof (likely the one known to Hilbert) uses the fact that the finite extensions of C(z) correspond to compact Riemann surfaces realized as branched covers of the Riemann sphere C^, which ^ in turn are described by the fundamental group π1(D) of domains D = C r fz1; : : : ; zdg, where z1; : : : ; zd are the branch points. -
An Arithmetic Riemann-Roch Theorem for Pointed Stable Curves
An arithmetic Riemann-Roch theorem for pointed stable curves Gerard Freixas i Montplet Abstract.- Let ( , Σ, F∞) be an arithmetic ring of Krull dimension at most 1, O = Spec and (π : ; σ1,...,σ ) a n-pointed stable curve of genus g. Write S O X → S n = σ ( ). The invertible sheaf ωX S(σ1 + ... + σ ) inherits a hermitian struc- U X \ ∪j j S / n ture hyp from the dual of the hyperbolic metric on the Riemann surface ∞. In this articlek·k we prove an arithmetic Riemann-Roch type theorem that computes theU arith- metic self-intersection of ωX /S(σ1 + ... + σn)hyp. The theorem is applied to modular curves X(Γ), Γ = Γ0(p) or Γ1(p), p 11 prime, with sections given by the cusps. We ′ a b c ≥ show Z (Y (Γ), 1) e π Γ2(1/2) L(0, Γ), with p 11 mod 12 when Γ = Γ0(p). Here Z(Y (Γ),s) is the Selberg∼ zeta functionM of the open modular≡ curve Y (Γ), a,b,c are rational numbers, Γ is a suitable Chow motive and means equality up to algebraic unit. M ∼ Resum´ e.-´ Soit ( , Σ, F∞) un anneau arithm´etique de dimension de Krull au plus 1, O = Spec et (π : ; σ1,...,σ ) une courbe stable n-point´ee de genre g. Posons S O X → S n = σ ( ). Le faisceau inversible ωX S(σ1+...+σ ) h´erite une structure hermitienne U X \∪j j S / n hyp du dual de la m´etrique hyperbolique sur la surface de Riemann ∞. Dans cet article nousk·k prouvons un th´eor`eme de Riemann-Roch arithm´etique qui calculeU l’auto-intersection arithm´etique de ωX /S(σ1 + ...+ σn)hyp. -
NNALES SCIEN IFIQUES SUPÉRIEU E D L ÉCOLE ORMALE
ISSN 0012-9593 ASENAH quatrième série - tome 42 fascicule 2 mars-avril 2009 NNALES SCIENIFIQUES d L ÉCOLE ORMALE SUPÉRIEUE Gérard FREIXAS i MONTPLET An arithmetic Riemann-Roch theorem for pointed stable curves SOCIÉTÉ MATHÉMATIQUE DE FRANCE Ann. Scient. Éc. Norm. Sup. 4 e série, t. 42, 2009, p. 335 à 369 AN ARITHMETIC RIEMANN-ROCH THEOREM FOR POINTED STABLE CURVES ʙʏ Gʀʀ FREIXAS ɪ MONTPLET Aʙʀ. – Let ( , Σ,F ) be an arithmetic ring of Krull dimension at most 1, =Spec and O ∞ S O (π : ; σ1,...,σn) an n-pointed stable curve of genus g. Write = j σj ( ). The invertible X→S U X\∪ S sheaf ω / (σ1 + + σn) inherits a hermitian structure hyp from the dual of the hyperbolic met- X S ··· · ric on the Riemann surface . In this article we prove an arithmetic Riemann-Roch type theorem U∞ that computes the arithmetic self-intersection of ω / (σ1 + + σn)hyp. The theorem is applied to X S ··· modular curves X(Γ), Γ=Γ0(p) or Γ1(p), p 11 prime, with sections given by the cusps. We show a b c ≥ Z(Y (Γ), 1) e π Γ2(1/2) L(0, Γ), with p 11 mod 12 when Γ=Γ0(p). Here Z(Y (Γ),s) is ∼ M ≡ the Selberg zeta function of the open modular curve Y (Γ), a, b, c are rational numbers, Γ is a suitable M Chow motive and means equality up to algebraic unit. ∼ R. – Soient ( , Σ,F ) un anneau arithmétique de dimension de Krull au plus 1, O ∞ =Spec et (π : ; σ1,...,σn) une courbe stable n-pointée de genre g. -
Automorphy of Mod 2 Galois Representations Associated to Certain Genus 2 Curves Over Totally Real Fields
AUTOMORPHY OF MOD 2 GALOIS REPRESENTATIONS ASSOCIATED TO CERTAIN GENUS 2 CURVES OVER TOTALLY REAL FIELDS ALEXANDRU GHITZA AND TAKUYA YAMAUCHI Abstract. Let C be a genus two hyperelliptic curve over a totally real field F . We show that the mod 2 Galois representation ρC;2 : Gal(F =F ) −! GSp4(F2) attached to C is automorphic when the image of ρC;2 is isomorphic to S5 and it is also a transitive subgroup under a fixed isomorphism GSp4(F2) ' S6. To be more precise, there exists a Hilbert{Siegel Hecke eigen cusp form h on GSp4(AF ) of parallel weight two whose mod 2 Galois representation ρh;2 is isomorphic to ρC;2. 1. Introduction Let K be a number field in an algebraic closure Q of Q and p be a prime number. Fix an embedding Q ,! C and an isomorphism Qp ' C. Let ι = ιp : Q −! Qp be an embedding that is compatible with the maps Q ,! C and Qp ' C fixed above. In proving automorphy of a given geometric p-adic Galois representation ρ : GK := Gal(Q=K) −! GLn(Qp); a standard way is to observe automorphy of its residual representation ρ : GK −! GLn(Fp) after choosing a suitable integral lattice. However, proving automorphy of ρ is hard unless the image of ρ is small. If the image is solvable, one can use the Langlands base change argument to find an automorphic cuspidal representation as is done in many known cases. Beyond this, one can ask that p and the image of ρ be small enough that one can apply the known cases of automorphy of Artin representations (cf. -
Inverse Galois Problem for Totally Real Number Fields
Cornell University Mathematics Department Senior Thesis Inverse Galois Problem for Totally Real Number Fields Sudesh Kalyanswamy Class of 2012 April, 2012 Advisor: Prof. Ravi Ramakrishna, Department of Mathematics Abstract In this thesis we investigate a variant of the Inverse Galois Problem. Namely, given a finite group G, the goal is to find a totally real extension K=Q, neces- sarily finite, such that Gal(K=Q) is isomorphic to G. Questions regarding the factoring of primes in these extensions also arise, and we address these where possible. The first portion of this thesis is dedicated to proving and developing the requisite algebraic number theory. We then prove the existence of totally real extensions in the cases where G is abelian and where G = Sn for some n ≥ 2. In both cases, some explicit polynomials with Galois group G are provided. We obtain the existence of totally real G-extensions of Q for all groups of odd order using a theorem of Shafarevich, and also outline a method to obtain totally real number fields with Galois group D2p, where p is an odd prime. In the abelian setting, we consider the factorization of primes of Z in the con- structed totally real extensions. We prove that the primes 2 and 5 each split in infinitely many totally real Z=3Z-extensions, and, more generally, that for primes p and q, p will split in infinitely many Z=qZ-extensions of Q. Acknowledgements I would like to thank Professor Ravi Ramakrishna for all his guidance and support throughout the year, as well as for the time he put into reading and editing the thesis. -
Inverse Galois Problem Research Report in Mathematics, Number 13, 2017
ISSN: 2410-1397 Master Dissertation in Mathematics Inverse Galois Problem University of Nairobi Research Report in Mathematics, Number 13, 2017 James Kigunda Kabori August 2017 School of Mathematics Submied to the School of Mathematics in partial fulfilment for a degree in Master of Science in Pure Mathematics Master Dissertation in Mathematics University of Nairobi August 2017 Inverse Galois Problem Research Report in Mathematics, Number 13, 2017 James Kigunda Kabori School of Mathematics College of Biological and Physical sciences Chiromo, o Riverside Drive 30197-00100 Nairobi, Kenya Master Thesis Submied to the School of Mathematics in partial fulfilment for a degree in Master of Science in Pure Mathematics Prepared for The Director Board Postgraduate Studies University of Nairobi Monitored by Director, School of Mathematics ii Abstract The goal of this project, is to study the Inverse Galois Problem. The Inverse Galois Problem is a major open problem in abstract algebra and has been extensive studied. This paper by no means proves the Inverse Galois Problem to hold or not to hold for all nite groups but we will, in chapter 4, show generic polynomials over Q satisfying the Inverse Galois Problem. Master Thesis in Mathematics at the University of Nairobi, Kenya. ISSN 2410-1397: Research Report in Mathematics ©Your Name, 2017 DISTRIBUTOR: School of Mathematics, University of Nairobi, Kenya iv Declaration and Approval I the undersigned declare that this dissertation is my original work and to the best of my knowledge, it has not been submitted in support of an award of a degree in any other university or institution of learning. -
SPECIALIZATIONS of GALOIS COVERS of the LINE 11 It Is the Condition (Κ-Big-Enough) from Proposition 2.2 of [DG10] That Needs to Be Satisfied)
SPECIALIZATIONS OF GALOIS COVERS OF THE LINE PIERRE DEBES` AND NOUR GHAZI Abstract. The main topic of the paper is the Hilbert-Grunwald property of Galois covers. It is a property that combines Hilbert’s irreducibility theorem, the Grunwald problem and inverse Galois theory. We first present the main results of our preceding paper which concerned covers over number fields. Then we show how our method can be used to unify earlier works on specializations of covers over various fields like number fields, PAC fields or finite fields. Finally we consider the case of rational function fields κ(x) and prove a full analog of the main theorem of our preceding paper. 1. Inroduction The Hilbert-Grunwald property of Galois covers over number fields was defined and studied in our previous paper [DG10]. It combines several topics: the Grunwald-Wang problem, Hilbert’s irreducibility theorem and the Regular Inverse Galois Problem (RIGP). Roughly speaking our main result there, which is recalled below as theorem 2.1 showed how, under certain conditions, a Galois cover f : X → P1 provides, by specialization, solutions to Grunwald problems. We next explained how to deduce an obstruction (possibly vacuous) for a finite group to be a regular Galois group over some number field K, i.e. the Galois group of some regular Galois extension E/K(T ) (corollary 1.5 of [DG10]). A refined form of this obstruction led us to some statements that question the validity of the Regular Inverse Galois Problem (RIGP) (corollaries 1.6 and 4.1 of [DG10]). The aim of this paper is threefold: - in §2: we present in more details the contents of [DG10]. -
The Inverse Galois Problem Over Formal Power Series Fields by Moshe Jarden, Tel Aviv University Israel Journal of Mathematics 85
The inverse Galois problem over formal power series fields by Moshe Jarden, Tel Aviv University Israel Journal of Mathematics 85 (1994), 263–275. Introduction The inverse Galois problem asks whether every finite group G occurs as a Galois group over the field Q of rational numbers. We then say that G is realizable over Q. This problem goes back to Hilbert [Hil] who realized Sn and An over Q. Many more groups have been realized over Q since 1892. For example, Shafarevich [Sha] finished in 1958 the work started by Scholz 1936 [Slz] and Reichardt 1937 [Rei] and realized all solvable groups over Q. The last ten years have seen intensified efforts toward a positive solution of the problem. The area has become one of the frontiers of arithmetic geometry (see surveys of Matzat [Mat] and Serre [Se1]). Parallel to the effort of realizing groups over Q, people have generalized the inverse Galois problem to other fields with good arithmetical properties. The most distinguished field where the problem has an affirmative solution is C(t). This is a consequence of the Riemann Existence Theorem from complex analysis. Winfried Scharlau and Wulf-Dieter Geyer asked what is the absolute Galois group of the field of formal power series F = K((X1,...,Xr)) in r ≥ 2 variables over an arbitrary field K. The full answer to this question is still out of reach. However, a theorem of Harbater (Proposition 1.1a) asserts that each Galois group is realizable over the field of rational function F (T ). By a theorem of Weissauer (Proposition 3.1), F is Hilbertian. -
Inverse Galois Problem and Significant Methods
Inverse Galois Problem and Significant Methods Fariba Ranjbar*, Saeed Ranjbar * School of Mathematics, Statistics and Computer Science, University of Tehran, Tehran, Iran. [email protected] ABSTRACT. The inverse problem of Galois Theory was developed in the early 1800’s as an approach to understand polynomials and their roots. The inverse Galois problem states whether any finite group can be realized as a Galois group over ℚ (field of rational numbers). There has been considerable progress in this as yet unsolved problem. Here, we shall discuss some of the most significant results on this problem. This paper also presents a nice variety of significant methods in connection with the problem such as the Hilbert irreducibility theorem, Noether’s problem, and rigidity method and so on. I. Introduction Galois Theory was developed in the early 1800's as an approach to understand polynomials and their roots. Galois Theory expresses a correspondence between algebraic field extensions and group theory. We are particularly interested in finite algebraic extensions obtained by adding roots of irreducible polynomials to the field of rational numbers. Galois groups give information about such field extensions and thus, information about the roots of the polynomials. One of the most important applications of Galois Theory is solvability of polynomials by radicals. The first important result achieved by Galois was to prove that in general a polynomial of degree 5 or higher is not solvable by radicals. Precisely, he stated that a polynomial is solvable by radicals if and only if its Galois group is solvable. According to the Fundamental Theorem of Galois Theory, there is a correspondence between a polynomial and its Galois group, but this correspondence is in general very complicated. -
Bibliography
Bibliography Comments Introductory sources on related subjects. local fields [Cas]; algebraic number theory [KKS], [M], [N5], [NSchW], [CF], [FT], [BSh], [Iya], [La2], [IR], [Ko6], [W]; cyclotomic fields [Wa], [La3]; valuation theory [E], [Rib]; history of [Roq3]; formally -adic fields [PR]; non-Archimedean analysis [Kob1–2], [vR], [Schf], [T4], [BGR]; embedding problems [ILF]; formal groups [Fr], [CF], [Iw6], [Haz3]; elliptic curves over number fields [Silv]; local zeta function and Fourier analysis [T1], [RV], [Ig], [Den]; -adic ¡ -functions [Wa], [Iw7], [Hi]; local Langlands correspondence [T7], [Bum], [Kudl], [BaK], [Rit2]; pro- -groups [DdSMS], [Wi], [dSSS]; -adic Hodge theory [T2], [Fo2], [Sen4,7–9]; -adic periods [A]; -adic differential equations [RC]; non-Archimedean analytic geometry [Ber]; field arithmetic [FJ], [Jar], [Ef4]; characteristic [Gos]; Milnor ¢ -theory [Bas], [Ro], [Silr], [Gr]; higher local fields and higher local class field theory [FK]; power series over local fields, formal groups, and dynamics [Lu1–2], [Li1–4]; non-Archimedean physics [VVZ], [BF], [Chr], [RTVW], [HS], [Kh]. Symbols and explicit formulas (perfect residue field case). [AH1–2], [Has1–11], [Sha2], [Kn], [Rot], [Bru1–2], [Henn1–2], [Iw3], [Col1,3], [Wil], [CW1], [dSh1–3], [Sen3], [Hel], [Des], [Shi], [Sue], [ShI], [V1–7,9], [Fe1–2], [BeV1–2], [Ab5–6], [Kol], [Kuz], [Kat6–7], [Ku3–4], [GK], [VG], [DV1–2], [Ben1–2]. 319 320 £¥¤§¦©¨ ¤ © Ramification theory of local fields (perfect residue field case). [Kaw1], [Sa], [Tam], [Hei], [Mar1], [Mau1–5], [Mik5–6], [T2], [Wy], [Sen1–2], [ST], [Ep], [KZ], [Fo4], [Win1–4], [Lau1–6], [LS], [CG], [Ab2–4,7–8], [Fe8,11–12]. Bibliography [A] Periodes´ -adiques, Asterisque´ , vol. 223, SMF, 1994.