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Expander graphs in pure and applied mathematics
 Bull. Amer. Math. Soc. (N.S
"... Expander graphs are highly connected sparse finite graphs. They play an important role in computer science as basic building blocks for network constructions, error correcting codes, algorithms and more. In recent years they have started to play an increasing role also in pure mathematics: number th ..."
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Expander graphs are highly connected sparse finite graphs. They play an important role in computer science as basic building blocks for network constructions, error correcting codes, algorithms and more. In recent years they have started to play an increasing role also in pure mathematics: number theory, group theory, geometry and more. This expository article describes their constructions and various applications in pure and applied mathematics. This paper is based on notes prepared for the Colloquium Lectures at the
Average twin prime conjecture for elliptic curves
, 2007
"... Let E be an elliptic curve over Q. In 1988, Koblitz conjectured a precise asymptotic for the number of primes p up to x such that the order of the group of points of E over Fp is prime. This is an analogue of the Hardy and Littlewood twin prime conjecture in the case of elliptic curves. Koblitz’s co ..."
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Cited by 7 (3 self)
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Let E be an elliptic curve over Q. In 1988, Koblitz conjectured a precise asymptotic for the number of primes p up to x such that the order of the group of points of E over Fp is prime. This is an analogue of the Hardy and Littlewood twin prime conjecture in the case of elliptic curves. Koblitz’s conjecture is still widely open. In this paper we prove that Koblitz’s conjecture is true on average over a twoparameter family of elliptic curves. One of the key ingredients in the proof is a short average distribution result in the style of BarbanDavenportHalberstam,
Sur un problème de Gelfond: la somme des chiffres des nombres premiers
, 2010
"... In this article we answer a question proposed by Gelfond in 1968. We prove that the sum of digits of prime numbers written in a basis q> 2 is equidistributed in arithmetic progressions (except for some well known degenerate cases). We prove also that the sequence.˛sq.p/ / where p runs through the p ..."
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Cited by 7 (1 self)
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In this article we answer a question proposed by Gelfond in 1968. We prove that the sum of digits of prime numbers written in a basis q> 2 is equidistributed in arithmetic progressions (except for some well known degenerate cases). We prove also that the sequence.˛sq.p/ / where p runs through the prime numbers is equidistributed modulo 1 if and only if ˛ 2 � n �.
The hyperbolic lattice point count in infinite volume with applications to sieves
 arXive:0712.139, 2008. CIRCLE PACKING 50
"... Abstract. We develop novel techniques using only abstract operator theory to obtain asymptotic formulae for lattice counting problems on infinitevolume hyperbolic manifolds, with error terms which are uniform as the lattice moves through “congruence ” subgroups. We give the following application to ..."
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Abstract. We develop novel techniques using only abstract operator theory to obtain asymptotic formulae for lattice counting problems on infinitevolume hyperbolic manifolds, with error terms which are uniform as the lattice moves through “congruence ” subgroups. We give the following application to the theory of affine linear sieves. In the spirit of Fermat, consider the problem of primes in the sum of two squares, f(c, d) = c2 + d2, but restrict (c, d) to the orbit O = (0, 1)Γ, where Γ is an infiniteindex nonelementary finitelygenerated subgroup of SL(2, Z) containing unipotent elements. We show that the set of values f(O) contains infinitely many integers having at most R prime factors for any R> 4/(δ−θ), where θ> 1/2 is the spectral gap and δ < 1 is the Hausdorff dimension of the limit set of Γ. If δ> 149/150, then we can take θ = 5/6, giving R = 25. The limit of this method is R = 9 for δ − θ> 4/9. This is the same number of prime factors as attained in Brun’s original attack on the twin prime conjecture. 1.
Reductions of an elliptic curve with almost prime orders
"... 1 Let E be an elliptic curve over Q. For a prime p of good reduction, let Ep be the reduction of E modulo p. We investigate Koblitz’s Conjecture about the number of primes p for which Ep(Fp) has prime order. More precisely, our main result is that if E is with Complex Multiplication, then there exis ..."
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1 Let E be an elliptic curve over Q. For a prime p of good reduction, let Ep be the reduction of E modulo p. We investigate Koblitz’s Conjecture about the number of primes p for which Ep(Fp) has prime order. More precisely, our main result is that if E is with Complex Multiplication, then there exist infinitely many primes p for which #Ep(Fp) has at most 5 prime factors. We also obtain upper bounds for the number of primes p ≤ x for which #Ep(Fp) is a prime. 1
Prime pairs and zeta’s zeros
, 2007
"... Abstract. There is extensive numerical support for the primepair conjecture (PPC) of Hardy and Littlewood (1923) on the asymptotic behavior of π2r(x), the number of prime pairs (p, p + 2r) with p ≤ x. However, it is still not known whether there are infinitely many prime pairs with given even diffe ..."
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Abstract. There is extensive numerical support for the primepair conjecture (PPC) of Hardy and Littlewood (1923) on the asymptotic behavior of π2r(x), the number of prime pairs (p, p + 2r) with p ≤ x. However, it is still not known whether there are infinitely many prime pairs with given even difference! Using a strong hypothesis on (weighted) equidistribution of primes in arithmetic progressions, Goldston, Pintz and Yildirim have recently shown that there are infinitely many pairs of primes differing by at most sixteen. The present author uses a Tauberian approach to derive that the PPC is equivalent to specific boundary behavior of certain functions involving zeta’s complex zeros. Under Riemann’s Hypothesis (RH) and on the real axis these functions resemble paircorrelation expressions. A speculative extension of Montgomery’s classical work (1973) would imply that there must be an abundance of prime pairs. 1.
A PSEDUOTWIN PRIMES THEOREM
"... The Twin Prime Conjecture states that there are infinitely many primes p such that p + 2 is also prime. A refined version of this conjecture is that π2(x), the number of prime twins lying below a level x, satisfies ..."
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The Twin Prime Conjecture states that there are infinitely many primes p such that p + 2 is also prime. A refined version of this conjecture is that π2(x), the number of prime twins lying below a level x, satisfies
CONTRIBUTIONS TO PROBABILITY PROBABILITY THEORY Lagrange’s Theorem and Thin Subsequences of Squares
"... Probabilistic methods are used to prove that for every E> 0 there exists a sequence A, of squares such that every positive integer is the sum of at most four squares in A, and A,(x) = 0(x=8 + y. Key words and phrases: Sums of squares, additive bases, probabilistic methods in additive number theory. ..."
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Probabilistic methods are used to prove that for every E> 0 there exists a sequence A, of squares such that every positive integer is the sum of at most four squares in A, and A,(x) = 0(x=8 + y. Key words and phrases: Sums of squares, additive bases, probabilistic methods in additive number theory. The set A of positive integers is a basis of order h if every positive integer is the sum of at most h elements of A. Lagrange proved in 1770 that the set of squares is a basis of order 4. Let A(x) denote the number of elements of
ADDITIVE PROBLEMS WITH PRIME VARIABLES THE CIRCLE METHOD OF HARDY, RAMANUJAN AND LITTLEWOOD
"... ABSTRACT. In these lectures we give an overview of the circle method introduced by Hardy and Ramanujan at the beginning of the twentieth century, and developed by Hardy, Littlewood and Vinogradov, among others. We also try and explain the main difficulties in proving Goldbach’s conjecture and we giv ..."
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ABSTRACT. In these lectures we give an overview of the circle method introduced by Hardy and Ramanujan at the beginning of the twentieth century, and developed by Hardy, Littlewood and Vinogradov, among others. We also try and explain the main difficulties in proving Goldbach’s conjecture and we give a sketch of the proof of Vinogradov’s threeprime Theorem. 1. ADDITIVE PROBLEMS In the last few centuries many additive problems have come to the attention of mathematicians: famous examples are Waring’s problem and Goldbach’s conjecture. In general, an additive problem can be expressed in the following form: we are given s ≥ 2 subsets of the set of natural numbers N, not necessarily distinct, which we call A1,..., As. We would like to determine the number of solutions of the equation n = a1 + a2 + ·· · + as (1.1) for a given n ∈ N, with the constraint that a j ∈ A j for j = 1,..., s, or, failing that, we would like to prove that the same equation has at least one solution for “sufficiently large ” n. In fact, we can not expect, in general, that for very small n there will be a solution of equation (1.1). Furthermore, depending on the nature of the sets A j, there may be some arithmetical constraints
Preface Lectures on sieves
, 2002
"... These are notes of a series of lectures on sieves, presented during the Special ..."
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These are notes of a series of lectures on sieves, presented during the Special