A Zero Density Estimate for Dedekind Zeta Functions 3
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Arithmetic Equivalence and Isospectrality
ARITHMETIC EQUIVALENCE AND ISOSPECTRALITY ANDREW V.SUTHERLAND ABSTRACT. In these lecture notes we give an introduction to the theory of arithmetic equivalence, a notion originally introduced in a number theoretic setting to refer to number fields with the same zeta function. Gassmann established a direct relationship between arithmetic equivalence and a purely group theoretic notion of equivalence that has since been exploited in several other areas of mathematics, most notably in the spectral theory of Riemannian manifolds by Sunada. We will explicate these results and discuss some applications and generalizations. 1. AN INTRODUCTION TO ARITHMETIC EQUIVALENCE AND ISOSPECTRALITY Let K be a number field (a finite extension of Q), and let OK be its ring of integers (the integral closure of Z in K). The Dedekind zeta function of K is defined by the Dirichlet series X s Y s 1 ζK (s) := N(I)− = (1 N(p)− )− I OK p − ⊆ where the sum ranges over nonzero OK -ideals, the product ranges over nonzero prime ideals, and N(I) := [OK : I] is the absolute norm. For K = Q the Dedekind zeta function ζQ(s) is simply the : P s Riemann zeta function ζ(s) = n 1 n− . As with the Riemann zeta function, the Dirichlet series (and corresponding Euler product) defining≥ the Dedekind zeta function converges absolutely and uniformly to a nonzero holomorphic function on Re(s) > 1, and ζK (s) extends to a meromorphic function on C and satisfies a functional equation, as shown by Hecke [25]. The Dedekind zeta function encodes many features of the number field K: it has a simple pole at s = 1 whose residue is intimately related to several invariants of K, including its class number, and as with the Riemann zeta function, the zeros of ζK (s) are intimately related to the distribution of prime ideals in OK . -
Artin L-Functions
Artin L-functions Charlotte Euvrard Laboratoire de Mathématiques de Besançon January 10, 2014 Charlotte Euvrard (LMB) Artin L-functions Atelier PARI/GP 1 / 12 Definition L=K Galois extension of number fields G = Gal(L=K ) its Galois group Let (r;V ) be a representation of G and c the associated character. Let p be a prime ideal in the ring of integers OK of K , we denote by : Ip the inertia group jp the Frobenius automorphism I V p = fv 2 V : 8i 2 Ip; r(i)(v) = vg Charlotte Euvrard (LMB) Artin L-functions Atelier PARI/GP 2 / 12 1 In the particular case K = Q : L(s;c;L=Q) = ∏ det(Id − p−sj ;V Ip ) p2Z p Definition Definition The Artin L-function is defined by : 1 L(s; ;L=K ) = ; Re(s) > 1; c ∏ −s I det(Id − N(p) jp;V p ) p⊂OK where 8 −s < det(Id − N(p) r(jp)) if p is unramified −s Ip −s I det(Id−N(p) jp;V ) = det(Id − N(p) r~(jp)) if p is ramified and V p 6= f0g : 1 otherwise and 1 r~(s¯) = r(js) jI j ∑ p j2Ip Charlotte Euvrard (LMB) Artin L-functions Atelier PARI/GP 3 / 12 Definition Definition The Artin L-function is defined by : 1 L(s; ;L=K ) = ; Re(s) > 1; c ∏ −s I det(Id − N(p) jp;V p ) p⊂OK where 8 −s < det(Id − N(p) r(jp)) if p is unramified −s Ip −s I det(Id−N(p) jp;V ) = det(Id − N(p) r~(jp)) if p is ramified and V p 6= f0g : 1 otherwise and 1 r~(s¯) = r(js) jI j ∑ p j2Ip 1 In the particular case K = Q : L(s;c;L=Q) = ∏ det(Id − p−sj ;V Ip ) p2Z p Charlotte Euvrard (LMB) Artin L-functions Atelier PARI/GP 3 / 12 Sum and Euler product Proposition Let d and d0 be the degrees of the representations (r;V ) and (r~;V Ip ). -
Part III Essay on Serre's Conjecture
Serre’s conjecture Alex J. Best June 2015 Contents 1 Introduction 2 2 Background 2 2.1 Modular forms . 2 2.2 Galois representations . 6 3 Obtaining Galois representations from modular forms 13 3.1 Congruences for Ramanujan’s t function . 13 3.2 Attaching Galois representations to general eigenforms . 15 4 Serre’s conjecture 17 4.1 The qualitative form . 17 4.2 The refined form . 18 4.3 Results on Galois representations associated to modular forms 19 4.4 The level . 21 4.5 The character and the weight mod p − 1 . 22 4.6 The weight . 24 4.6.1 The level 2 case . 25 4.6.2 The level 1 tame case . 27 4.6.3 The level 1 non-tame case . 28 4.7 A counterexample . 30 4.8 The proof . 31 5 Examples 32 5.1 A Galois representation arising from D . 32 5.2 A Galois representation arising from a D4 extension . 33 6 Consequences 35 6.1 Finiteness of classes of Galois representations . 35 6.2 Unramified mod p Galois representations for small p . 35 6.3 Modularity of abelian varieties . 36 7 References 37 1 1 Introduction In 1987 Jean-Pierre Serre published a paper [Ser87], “Sur les representations´ modulaires de degre´ 2 de Gal(Q/Q)”, in the Duke Mathematical Journal. In this paper Serre outlined a conjecture detailing a precise relationship between certain mod p Galois representations and specific mod p modular forms. This conjecture and its variants have become known as Serre’s conjecture, or sometimes Serre’s modularity conjecture in order to distinguish it from the many other conjectures Serre has made. -
A Refinement of the Artin Conductor and the Base Change Conductor
A refinement of the Artin conductor and the base change conductor C.-L. Chai and C. Kappen Abstract For a local field K with positive residue characteristic p, we introduce, in the first part of this paper, a refinement bArK of the classical Artin distribution ArK . It takes values in cyclotomic extensions of Q which are unramified at p, and it bisects ArK in the sense that ArK is equal to the sum of bArK and its conjugate distribution. 1 Compared with 2 ArK , the bisection bArK provides a higher resolution on the level of tame ramification. In the second part of this article, we prove that the base change conductor c(T ) of an analytic K-torus T is equal to the value of bArK on the Qp-rational ∗ ∗ Galois representation X (T ) ⊗Zp Qp that is given by the character module X (T ) of T . We hereby generalize a formula for the base change conductor of an algebraic K-torus, and we obtain a formula for the base change conductor of a semiabelian K-variety with potentially ordinary reduction. Contents 1 Introduction 1 2 Notation 4 3 A bisection of the Artin character 5 4 Analytic tori 15 5 The base change conductor 17 6 A formula for the base change conductor 24 7 Application to semiabelian varieties with potentially ordinary reduc- tion 27 References 30 1. Introduction The base change conductor c(A) of a semiabelian variety A over a local field K is an interesting arithmetic invariant; it measures the growth of the volume of the N´eron model of A under base change, cf. -
L-FUNCTIONS Contents Introduction 1 1. Algebraic Number Theory 3 2
L-FUNCTIONS ALEKSANDER HORAWA Contents Introduction1 1. Algebraic Number Theory3 2. Hecke L-functions 10 3. Tate's Thesis: Fourier Analysis in Number Fields and Hecke's Zeta Functions 13 4. Class Field Theory 52 5. Artin L-functions 55 References 79 Introduction These notes, meant as an introduction to the theory of L-functions, form a report from the author's Undergraduate Research Opportunities project at Imperial College London under the supervision of Professor David Helm. The theory of L-functions provides a way to study arithmetic properties of integers (and, more generally, integers of number fields) by first, translating them to analytic properties of certain functions, and then, using the tools and methods of analysis, to study them in this setting. The first indication that the properties of primes could be studied analytically came from Euler, who noticed the factorization (for a real number s > 1): 1 X 1 Y 1 = : ns 1 − p−s n=1 p prime This was later formalized by Riemann, who defined the ζ-function by 1 X 1 ζ(s) = ns n=1 for a complex number s with Re(s) > 1 and proved that it admits an analytic continuation by means of a functional equation. Riemann established a connection between its zeroes and the distribution of prime numbers, and it was also proven that the Prime Number Theorem 1 2 ALEKSANDER HORAWA is equivalent to the fact that no zeroes of ζ lie on the line Re(s) = 1. Innocuous as it may seem, this function is very difficult to study (the Riemann Hypothesis, asserting that the 1 non-trivial zeroes of ζ lie on the line Re(s) = 2 , still remains one of the biggest open problems in mathematics). -
Introduction to L-Functions: Dedekind Zeta Functions
Introduction to L-functions: Dedekind zeta functions Paul Voutier CIMPA-ICTP Research School, Nesin Mathematics Village June 2017 Dedekind zeta function Definition Let K be a number field. We define for Re(s) > 1 the Dedekind zeta function ζK (s) of K by the formula X −s ζK (s) = NK=Q(a) ; a where the sum is over all non-zero integral ideals, a, of OK . Euler product exists: Y −s −1 ζK (s) = 1 − NK=Q(p) ; p where the product extends over all prime ideals, p, of OK . Re(s) > 1 Proposition For any s = σ + it 2 C with σ > 1, ζK (s) converges absolutely. Proof: −n Y −s −1 Y 1 jζ (s)j = 1 − N (p) ≤ 1 − = ζ(σ)n; K K=Q pσ p p since there are at most n = [K : Q] many primes p lying above each rational prime p and NK=Q(p) ≥ p. A reminder of some algebraic number theory If [K : Q] = n, we have n embeddings of K into C. r1 embeddings into R and 2r2 embeddings into C, where n = r1 + 2r2. We will label these σ1; : : : ; σr1 ; σr1+1; σr1+1; : : : ; σr1+r2 ; σr1+r2 . If α1; : : : ; αn is a basis of OK , then 2 dK = (det (σi (αj ))) : Units in OK form a finitely-generated group of rank r = r1 + r2 − 1. Let u1;:::; ur be a set of generators. For any embedding σi , set Ni = 1 if it is real, and Ni = 2 if it is complex. Then RK = det (Ni log jσi (uj )j)1≤i;j≤r : wK is the number of roots of unity contained in K. -
SMALL ISOSPECTRAL and NONISOMETRIC ORBIFOLDS of DIMENSION 2 and 3 Introduction. in 1966
SMALL ISOSPECTRAL AND NONISOMETRIC ORBIFOLDS OF DIMENSION 2 AND 3 BENJAMIN LINOWITZ AND JOHN VOIGHT ABSTRACT. Revisiting a construction due to Vigneras,´ we exhibit small pairs of orbifolds and man- ifolds of dimension 2 and 3 arising from arithmetic Fuchsian and Kleinian groups that are Laplace isospectral (in fact, representation equivalent) but nonisometric. Introduction. In 1966, Kac [48] famously posed the question: “Can one hear the shape of a drum?” In other words, if you know the frequencies at which a drum vibrates, can you determine its shape? Since this question was asked, hundreds of articles have been written on this general topic, and it remains a subject of considerable interest [41]. Let (M; g) be a connected, compact Riemannian manifold (with or without boundary). Asso- ciated to M is the Laplace operator ∆, defined by ∆(f) = − div(grad(f)) for f 2 L2(M; g) a square-integrable function on M. The eigenvalues of ∆ on the space L2(M; g) form an infinite, discrete sequence of nonnegative real numbers 0 = λ0 < λ1 ≤ λ2 ≤ ::: , called the spectrum of M. In the case that M is a planar domain, the eigenvalues in the spectrum of M are essentially the frequencies produced by a drum shaped like M and fixed at its boundary. Two Riemannian manifolds are said to be Laplace isospectral if they have the same spectra. Inverse spectral geom- etry asks the extent to which the geometry and topology of M are determined by its spectrum. For example, volume, dimension and scalar curvature can all be shown to be spectral invariants. -
L-Functions and Non-Abelian Class Field Theory, from Artin to Langlands
L-functions and non-abelian class field theory, from Artin to Langlands James W. Cogdell∗ Introduction Emil Artin spent the first 15 years of his career in Hamburg. Andr´eWeil charac- terized this period of Artin's career as a \love affair with the zeta function" [77]. Claude Chevalley, in his obituary of Artin [14], pointed out that Artin's use of zeta functions was to discover exact algebraic facts as opposed to estimates or approxi- mate evaluations. In particular, it seems clear to me that during this period Artin was quite interested in using the Artin L-functions as a tool for finding a non- abelian class field theory, expressed as the desire to extend results from relative abelian extensions to general extensions of number fields. Artin introduced his L-functions attached to characters of the Galois group in 1923 in hopes of developing a non-abelian class field theory. Instead, through them he was led to formulate and prove the Artin Reciprocity Law - the crowning achievement of abelian class field theory. But Artin never lost interest in pursuing a non-abelian class field theory. At the Princeton University Bicentennial Conference on the Problems of Mathematics held in 1946 \Artin stated that `My own belief is that we know it already, though no one will believe me { that whatever can be said about non-Abelian class field theory follows from what we know now, since it depends on the behavior of the broad field over the intermediate fields { and there are sufficiently many Abelian cases.' The critical thing is learning how to pass from a prime in an intermediate field to a prime in a large field. -
On the Selberg Class of L-Functions
ON THE SELBERG CLASS OF L-FUNCTIONS ANUP B. DIXIT Abstract. The Selberg class of L-functions, S, introduced by A. Selberg in 1989, has been extensively studied in the past few decades. In this article, we give an overview of the structure of this class followed by a survey on Selberg's conjectures and the value distribution theory of elements in S. We also discuss a larger class of L-functions containing S, namely the Lindel¨ofclass, introduced by V. K. Murty. The Lindel¨ofclass forms a ring and its value distribution theory surprisingly resembles that of the Selberg class. 1. Introduction The most basic example of an L-function is the Riemann zeta-function, which was intro- duced by B. Riemann in 1859 as a function of one complex variable. It is defined on R s 1 as ∞ 1 ( ) > ζ s : s n=1 n It can be meromorphically continued to( the) ∶= wholeQ complex plane C with a pole at s 1 with residue 1. The unique factorization of natural numbers into primes leads to another representation of ζ s on R s 1, namely the Euler product = −1 1 ( ) ( ) > ζ s 1 : s p prime p The study of zeta-function is vital to( ) understanding= M − the distribution of prime numbers. For instance, the prime number theorem is a consequence of ζ s having a simple pole at s 1 and being non-zero on the vertical line R s 1. ( ) = In pursuing the analogous study of distribution( ) = of primes in an arithmetic progression, we consider the Dirichlet L-function, ∞ χ n L s; χ ; s n=1 n ( ) for R s 1, where χ is a Dirichlet character( ) ∶= moduloQ q, defined as a group homomorphism ∗ ∗ χ Z qZ C extended to χ Z C by periodicity and setting χ n 0 if n; q 1. -
Motives and Motivic L-Functions
Motives and Motivic L-functions Christopher Elliott December 6, 2010 1 Introduction This report aims to be an exposition of the theory of L-functions from the motivic point of view. The classical theory of pure motives provides a category consisting of `universal cohomology theories' for smooth projective varieties defined over { for instance { number fields. Attached to every motive we can define a function which is holomorphic on a subdomain of C which at least conjecturally satisfies similar properties to the Riemann zeta function: for instance meromorphic continuation and functional equation. The properties of this function are expected to encode deep arithmetic properties of the underlying variety. In particular, we will discuss a conjecture of Deligne and its more general forms due to Beilinson and others, that relates certain \special" values of the L-function { values at integer points { to a subtle arithmetic invariant called the regulator, vastly generalising the analytic class number formula. Finally I aim to describe potentially fruitful ways in which these exciting conjectures might be rephrased or reinterpreted, at least to make things clearer to me. There are several sources from which I have drawn ideas and material. In particular, the book [1] is a very good exposition of the theory of pure motives. For the material on L-functions, and in particular the Deligne and Beilinson conjectures, I referred to the surveys [9], [11] and [4] heavily. In particular, my approach to the Deligne conjecture follows the survey [11] of Schneider closely. Finally, when I motivate the definition of the motivic L-function I use the ideas and motivation in the introduction to the note [5] of Kim heavily. -
Serre's Modularity Conjecture
SERRE’S MODULARITY CONJECTURE (I) CHANDRASHEKHAR KHARE AND JEAN-PIERRE WINTENBERGER to Jean-Pierre Serre Abstract. This paper is the first part of a work which proves Serre’s modularity conjecture. We first prove the cases p 6= 2 and odd conduc- tor, and p = 2 and weight 2, see Theorem 1.2, modulo Theorems 4.1 and 5.1. Theorems 4.1 and 5.1 are proven in the second part, see [23]. We then reduce the general case to a modularity statement for 2-adic lifts of modular mod 2 representations. This statement is now a theorem of Kisin [28]. Contents 1. Introduction 2 1.1. Main result 2 1.2. The nature of the proof of Theorem 1.2 3 1.3. A comparison to the approach of [22] 3 1.4. Description of the paper 4 1.5. Notation 4 2. A crucial definition 4 3. Proof of Theorem 1.2 5 3.1. Auxiliary theorems 5 3.2. Proof of Theorem 1.2 6 4. Modularity lifting results 6 5. Compatible systems of geometric representations 7 6. Some utilitarian lemmas 10 7. Estimates on primes 12 8. Proofs of the auxiliary theorems 12 8.1. Proof of Theorem 3.1 12 8.2. Proof of Theorem 3.2 13 8.3. Proof of Theorem 3.3 15 8.4. Proof of Theorem 3.4 17 9. The general case 18 10. Modularity of compatible systems 19 CK was partially supported by NSF grants DMS 0355528 and DMS 0653821, the Miller Institute for Basic Research in Science, University of California Berkeley, and a Guggenheim fellowship. -
Algebraic Number Theory LTCC 2008 Lecture Notes, Part 3
Algebraic number theory LTCC 2008 Lecture notes, Part 3 7. The Riemann zeta function We write Re(z) for the real part of a complex number z 2 C. If a is a positive real number and z 2 C then az is de¯ned by az = exp(z ¢ log(a)). Note that ¡ ¢ jazj = jexp(z ¢ log(a))j = exp Re(z ¢ log(a)) = aRe(z): De¯nition 7.1. The Riemann zeta function ³(z) is the function de¯ned by X1 1 ³(z) = nz n=1 for z 2 C with Re(z) > 1. The absolute convergence of the series in the de¯nition of ³(z) follows easily by comparison to an integral, more precisely X1 ¯ ¯ X1 X1 ¯n¡z¯ = n¡Re(z) = 1 + n¡Re(z) n=1 n=1 Zn=2 1 1 < 1 + x¡Re(z)dx = 1 + : 1 Re(z) ¡ 1 The following theorem summarises some well-known facts about the Riemann zeta function. P1 ¡z Theorem 7.2. (1) The series n=1 n converges uniformly on sets of the form fz 2 C : Re(z) ¸ 1 + ±g with ± > 0. Therefore the function ³(z) is holomorphic on the set fz 2 C : Re(z) > 1g. (2) (Euler product) For all z 2 C with Re(z) > 1 we have Y 1 ³(z) = 1 ¡ p¡z p where the product runs over all prime numbers p. (3) (Analytic continuation) The function ³(z) can be extended to a meromorphic function on the whole complex plane. (4) (Functional equation) Let Z(z) = ¼¡z=2¡(z=2)³(z) where ¡ is the Gamma function.