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# Search by event  2256 | enregistrements trouvés : 28

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## Virtualconference  On S-Diophantine Tuples Ziegler, Volker (Auteur de la Conférence) | CIRM (Editeur )

Given a finite set of primes $S$ and a m-tuple $(a_{1},...,a_{m})$ of positive, distinct integers we call the m-tuple $S$-Diophantine, if for each 1 ≤ i < j ≤ m the quantity $a_{i}a_{j}+1$ has prime divisors coming only from the set $S$. In this talk we discuss the existence of m-tuples if the set of primes $S$ is small. We will discuss recent results concerning the case that $|S| = 2$ and $|S| = 3$.

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## Virtualconference  Poisson-generic points Weiss, Benjamin (Auteur de la Conférence) | CIRM (Editeur )

I will discuss a criterion for randomness of sequences of zeros and ones which is strictly stronger than normality, butholds for almost every sequence generated by i.i.d. random variables with distribution {1/2, 1/2}. Briefly put, the idea is count the number of times blocks of length n appear in the initial block of length $2^n$. I will also discuss an extension of this idea to toral automorphisms. (joint work with Yuval Peres)

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## Virtualconference  Classification and statistics of cut-and-project sets Weiss, Barak (Auteur de la Conférence) | CIRM (Editeur )

We introduce a class of so-called "Ratner-Marklof-Strombergsson measures". These are probability measures supported on cut-and-project sets in Euclidean space of dimension d>1 which are invariant and ergodic for the action of the groups ASL_d(R) or SL_d(R) (affine or linear maps preserving orientation and volume). We classify the measures that can arise in terms of algebraic groups and homogeneous dynamics. Using the classification, we prove analogues of results of Siegel, Weil and Rogers about a Siegel summation formula and identities and bounds involving higher moments. We deduce results about asymptotics, with error estimates, of point-counting and patchcounting for typical cut-and-project sets. Joint work with Rene Ruehr and Yotam Smilansky.
We introduce a class of so-called "Ratner-Marklof-Strombergsson measures". These are probability measures supported on cut-and-project sets in Euclidean space of dimension d>1 which are invariant and ergodic for the action of the groups ASL_d(R) or SL_d(R) (affine or linear maps preserving orientation and volume). We classify the measures that can arise in terms of algebraic groups and homogeneous dynamics. Using the classification, we prove ...

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## Virtualconference  On binary quartic Thue equations and related topics Walsh, Gary (Auteur de la Conférence) | CIRM (Editeur )

In a recent paper, Istvan Gaal and Laszlo Remete studied the integer solutions to binary quartic Thue equations of the form $x^4-dy^4 = \pm 1$, and used their results to determine pure quartic number fields which contain a power integral basis. In our talk, we propose a new way to approach this diophantine problem, and we also show how an effective version of the abc conjecture would allow for even further improvements. This is joint work with M.A. Bennett. We also discuss a relation between this quartic diophantine equation to recent joint work with P.-Z. Yuan.
In a recent paper, Istvan Gaal and Laszlo Remete studied the integer solutions to binary quartic Thue equations of the form $x^4-dy^4 = \pm 1$, and used their results to determine pure quartic number fields which contain a power integral basis. In our talk, we propose a new way to approach this diophantine problem, and we also show how an effective version of the abc conjecture would allow for even further improvements. This is joint work with ...

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## Virtualconference  Multidimensional continued fractions and symbolic codings of toral translations Thuswaldner, Jörg (Auteur de la Conférence) | CIRM (Editeur )

The aim of this lecture is to find good symbolic codings for translations on the $d$-dimensional torus that enjoy the well-known and nice properties of Sturmian sequences (as for instance low complexity and good local discrepancy properties, i.e., bounded remainder sets of any scale). Inspired by the approach of G. Rauzy we construct such codings by the use of multidimensional continued fraction algorithms that are realized by sequences of substitutions. This is joint work with V. Berthé and W. Steiner.
The aim of this lecture is to find good symbolic codings for translations on the $d$-dimensional torus that enjoy the well-known and nice properties of Sturmian sequences (as for instance low complexity and good local discrepancy properties, i.e., bounded remainder sets of any scale). Inspired by the approach of G. Rauzy we construct such codings by the use of multidimensional continued fraction algorithms that are realized by sequences of ...

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## Virtualconference  On generalised Rudin-Shapiro sequences Stoll, Thomas (Auteur de la Conférence) | CIRM (Editeur )

We introduce a family of block-additive automatic sequences, that are obtained by allocating a weight to each couple of digits, and defining the nth term of the sequence as being the total weight of the integer n written in base k. Under an additional combinatorial difference condition on the weight function, these sequences can be interpreted as generalised Rudin-Shapiro sequences. We prove that these sequences have the same two-term correlations as sequences of symbols chosen uniformly and independently at random. The speed of convergence is independent of the prime factor decomposition of k. This extends work by E. Grant, J. Shallit, T. Stoll, and by P.-A. Tahay.
We introduce a family of block-additive automatic sequences, that are obtained by allocating a weight to each couple of digits, and defining the nth term of the sequence as being the total weight of the integer n written in base k. Under an additional combinatorial difference condition on the weight function, these sequences can be interpreted as generalised Rudin-Shapiro sequences. We prove that these sequences have the same two-term c...

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## Virtualconference  Pseudorandomness at prime times and digits of Mersenne numbers Shparlinski, Igor (Auteur de la Conférence) | CIRM (Editeur )

We consider two common pseudorandom number generators constructed from iterations of linear and Möbius maps
$x \mapsto gx$ and $x \mapsto (ax+b)/(cx+d)$
over a residue ring modulo an integer q ≥ 2, which are known as congruential and inversive generators, respectively. There is an extensive literature on the pseudorandomness of elements $u_{n}, n=1,2,...$, of the corresponding orbits. In this talk we are interested in what happens in these orbits at prime times, that is, we study elements $u_{p}$, $p = 2, 3, . . .$, where $p$ runs over primes.
We give a short survey of previous results on the distribution of $u_{p}$ for the above maps and then:
- Explain how B. Kerr, L. Mérai and I. E. Shparlinski (2019) have used a method of N. M. Korobov (1972) to study the congruential generator on primes modulo a large power of a fixed prime, e.g. $q=3^{\gamma }$ with a large $\gamma$. We also give applications of this result to digits of Mersenne numbers $2^{p}-1$.
- Present a result of L. Mérai and I. E. Shparlinski (2020) on the distribution of the inversive generator on primes modulo a large prime, q. The proof takes advantage of the flexibility of Heath-Brown’s identity, while Vaughan’s identity does not seem to be enough for our purpose. We also pose several open questions and discuss links to Sarnak’s conjecture on pseudorandomness of the Möbius function.
We consider two common pseudorandom number generators constructed from iterations of linear and Möbius maps
$x \mapsto gx$ and $x \mapsto (ax+b)/(cx+d)$
over a residue ring modulo an integer q ≥ 2, which are known as congruential and inversive generators, respectively. There is an extensive literature on the pseudorandomness of elements $u_{n}, n=1,2,...$, of the corresponding orbits. In this talk we are interested in what happens in these ...

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## Virtualconference  Zaremba's conjecture and growth in groups Shkredov, Ilya (Auteur de la Conférence) | CIRM (Editeur )

Zaremba's conjecture belongs to the area of continued fractions. It predicts that for any given positive integer q there is a positive a, a < q, (a,q)=1 such that all partial quotients b_j in its continued fractions expansion a/q = 1/b_1+1/b_2 +... + 1/b_s are bounded by five. At the moment the question is widely open although the area has a rich history of works by Korobov, Hensley, Niederreiter, Bourgain and many others. We survey certain results concerning this hypothesis and show how growth in groups helps to solve different relaxations of Zaremba's conjecture. In particular, we show that a deeper hypothesis of Hensley concerning some Cantor-type set with the Hausdorff dimension >1/2 takes place for the so-called modular form of Zaremba's conjecture.
Zaremba's conjecture belongs to the area of continued fractions. It predicts that for any given positive integer q there is a positive a, a 1/2 takes place for the so-called modular form of Zaremba's conjecture....

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## Virtualconference  Large values of the remainder term of the prime number theorem Pintz, Janos (Auteur de la Conférence) | CIRM (Editeur )

In the lecture we prove a lower estimate for the average of the absolute value of the remainder term of the prime number theorem which depends in an explicit way on a given zero of the Riemann Zeta Function. The estimate is only interesting if this hypothetical zero lies off the critical line which naturally implies the falsity of the Riemann Hypothesis. (If the Riemann Hypothesis is true, stronger results areobtainable by other metods.) The first explicit results in this direction were proved by Turán and Knapowski in the 1950s, answering a problem of Littlewood from the year 1937. They used the power sum method of Turán. Our present approach does not use Turán’s method and gives sharper results.
In the lecture we prove a lower estimate for the average of the absolute value of the remainder term of the prime number theorem which depends in an explicit way on a given zero of the Riemann Zeta Function. The estimate is only interesting if this hypothetical zero lies off the critical line which naturally implies the falsity of the Riemann Hypothesis. (If the Riemann Hypothesis is true, stronger results areobtainable by other metods.) The ...

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## Virtualconference  Number of solutions to a special type of unit equations in two unknowns Pink, István (Auteur de la Conférence) | CIRM (Editeur )

For any fixed coprime positive integers a, b and c with min{a, b, c} > 1, we prove that the equation $a^{x}+b^{y}=c^{z}$ has at most two solutions in positive integers x, y and z, except for one specific case which exactly gives three solutions. Our result is essentially sharp in the sense that there are infinitely many examples allowing the equation to have two solutions in positive integers. From the viewpoint of a well-known generalization of Fermat’s equation, it is also regarded as a 3-variable generalization of the celebrated theorem of Bennett [M.A.Bennett, On some exponential equations of S.S.Pillai, Canad. J. Math. 53(2001), no.2, 897-922] which asserts that Pillai’s type equation $a^{x}-b^{y}=c$ has at most two solutions in positive integers x and y for any fixed positive integers a, b and c with min {a, b} > 1. In this talk we give a brief summary of corresponding earlier results and present the main improvements leading to this definitive result. This is a joint work with T. Miyazaki.
For any fixed coprime positive integers a, b and c with min{a, b, c} > 1, we prove that the equation $a^{x}+b^{y}=c^{z}$ has at most two solutions in positive integers x, y and z, except for one specific case which exactly gives three solutions. Our result is essentially sharp in the sense that there are infinitely many examples allowing the equation to have two solutions in positive integers. From the viewpoint of a well-known generalization of ...

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## Virtualconference  Bertini and Northcott Pazuki, Fabien (Auteur de la Conférence) | CIRM (Editeur )

I will report on joint work with Martin Widmer. Let X be a smooth projective variety over a number field K. We prove a Bertini-type theorem with explicit control of the genus, degree, height, and field of definition of the constructed curve on X. As a consequence we provide a general strategy to reduce certain height and rank estimates on abelian varieties over a number field K to the case of Jacobian varieties defined over a suitable extension of K. We will give examples where the strategy works well!
I will report on joint work with Martin Widmer. Let X be a smooth projective variety over a number field K. We prove a Bertini-type theorem with explicit control of the genus, degree, height, and field of definition of the constructed curve on X. As a consequence we provide a general strategy to reduce certain height and rank estimates on abelian varieties over a number field K to the case of Jacobian varieties defined over a suitable extension ...

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## Virtualconference  Dynamical irreducibility of polynomials modulo primes Ostafe, Alina (Auteur de la Conférence) | CIRM (Editeur )

In this talk we look at polynomials having the property that all compositional iterates are irreducible, which we call dynamical irreducible. After surveying some previous results (mostly over finite fields), we will concentrate on the question of the dynamical irreducibility of integer polynomials being preserved in reduction modulo primes. More precisely, for a class of integer polynomials $f$, which in particular includes all quadratic polynomials, and also trinomials of some special form, we show that, under some natural conditions, he set of primes $p$ such that $f$ is dynamical irreducible modulo $p$ is of relative density zero. The proof of this result relies on a combination of analytic (the square sieve) and diophantine (finiteness of solutions to certain hyperelliptic equations) tools, which we will briefly describe.
In this talk we look at polynomials having the property that all compositional iterates are irreducible, which we call dynamical irreducible. After surveying some previous results (mostly over finite fields), we will concentrate on the question of the dynamical irreducibility of integer polynomials being preserved in reduction modulo primes. More precisely, for a class of integer polynomials $f$, which in particular includes all quadratic ...

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## Virtualconference  Diophantine exponents, best approximation and badly approximable numbers Moshchevitin, Nikolay (Auteur de la Conférence) | CIRM (Editeur )

We will discuss recent progress in analysis of uniform and ordinary Diophantine exponents $\hat\omega$ and $\omega$ for linear Diophantine approximation as well as some applications of the related methods. In particular, we give a new criterion for badly approximable vectors in $\mathbb{R}^{d}$ the behavior of the best approximation vectors in the sense of simultaneous approximation and in the sense of linear form. It turned out that compared to the one-dimensional case our criterion is rather unusual. We apply this criterion to the analysis of Dirichlet spectrum for simultaneous Diophantine approximation.
We will discuss recent progress in analysis of uniform and ordinary Diophantine exponents $\hat\omega$ and $\omega$ for linear Diophantine approximation as well as some applications of the related methods. In particular, we give a new criterion for badly approximable vectors in $\mathbb{R}^{d}$ the behavior of the best approximation vectors in the sense of simultaneous approximation and in the sense of linear form. It turned out that compared ...

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## Virtualconference  Some interactions between number theory and multifractal analysis Martin, Bruno (Auteur de la Conférence) | CIRM (Editeur )

Some number-theoretic problems have led to the study of some infinite series that show multifractal behaviour, which means that their Hölder pointwise regularity may widely change from point to point. Reviewing some examples such as lacunary trigonometric series, Davenport series, Brjuno-type functions, I will put emphasis on the methods encountered in the literature to compute the pointwise Hölder exponent of such functions.

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## Virtualconference  The sum-of-digits function in linearly recurrent number systems and almost primes Madritsch, Manfred (Auteur de la Conférence) | CIRM (Editeur )

This is joint work with Jörg Thuswaldner from University of Leoben.

A linear recurrent number system is a generalization of the $q$-adic number system, where we replace the sequence of powers of $q$ by a linear recurrent sequence $G_{k+d}=a_1G_{k+d-1}+\cdots+a_dG_k$ for $k\geq 0$. Under some mild conditions on the recurrent sequence every positive integer $n$ has a representation of the form $n=\sum_{j=0}^k \varepsilon_j(n)G_j.$

The $q$-adic number system corresponds to the linear recursion $G_{k+1}=qG_k$ and $G_0=1$. The first example of a real generalization is due to Zeckendorf who showed that the Fibonacci sequence $G_0=1$, $G_1=2$, $G_{k+2}=G_{k+1}+G_k$ for $k\geq0$ yields a representation for each positive integer. This is unique if we additionally suppose that no two consecutive ones exist in the representation. Similar restrictions hold for different recurrent sequences and they build the essence of these number systems.

In the present talk we investigate the representation of primes and almost primes in linear recurrent number systems. We start by showing the different results due to Fouvry, Mauduit and Rivat in the case of $q$-adic number systems. Then we shed some light on their main tools and techniques. The heart of our considerations is the following Bombieri-Vinogradov type result
$\sum_{q < x^{\vartheta-\varepsilon}}\max_{y < x}\max_{1\leq a\leq q} \left\vert\sum_{\substack{n< y,s_G(n)\equiv b\bmod d\\ n\equiv b\bmod q}}1 -\frac1q\sum_{n < y,s_G(n)\equiv b\bmod d}1\right\vert \ll x(\log 2x)^{-A},$
which we establish under the assumption that $a_1\geq30$. This lower bound is due to numerical estimations. With this tool in hand we are able to show that $\left\vert\{n\leq x\colon s_G(n)\equiv b\bmod d, n=p_1\text{ or }n=p_1p_2\}\right\vert\gg \frac{x}{\log x}.$
This is joint work with Jörg Thuswaldner from University of Leoben.

A linear recurrent number system is a generalization of the $q$-adic number system, where we replace the sequence of powers of $q$ by a linear recurrent sequence $G_{k+d}=a_1G_{k+d-1}+\cdots+a_dG_k$ for $k\geq 0$. Under some mild conditions on the recurrent sequence every positive integer $n$ has a representation of the form $n=\sum_{j=0}^k \varepsilon_j(n)G_j.$

The $q$-adic ...

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## Virtualconference  Fibonacci numbers and repdigits Luca, Florian (Auteur de la Conférence) | CIRM (Editeur )

In the first part of the talk we will survey known results concerning Fibonacci numbers whose digital representations in base 10 display some interesting patterns. In the second part of the talk we will give the main steps of the proof of a recent result which states that $b = 4$ is the only integer ≥ 2 such that there are two Fibonacci numbers larger than 1 which are repunits in base b. In this case, $F_{5}=(4^{2}-1)/(4-1)$ and $F_{8}=(4^{3}-1)/(4-1)$. This is joint work with C. A. Gomez and J. C. Gomez from Cali, Colombia.

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