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# Documents  11G05 | enregistrements trouvés : 11

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## Post-edited  Formulas for the limiting distribution of traces of Frobenius Lachaud, Gilles (Auteur de la Conférence) | CIRM (Editeur )

We discuss the distribution of the trace of a random matrix in the compact Lie group USp2g, with the normalized Haar measure. According to the generalized Sato-Tate conjecture, if A is an abelian variety of dimension g defined over the rationals, the sequence of traces of Frobenius in the successive reductions of A modulo primes appears to be equidistributed with respect to this distribution. If g = 2, we provide expressions for the characteristic function, the density, and the repartition function of this distribution in terms of higher transcendental functions, namely Legendre and Meijer functions. We discuss the distribution of the trace of a random matrix in the compact Lie group USp2g, with the normalized Haar measure. According to the generalized Sato-Tate conjecture, if A is an abelian variety of dimension g defined over the rationals, the sequence of traces of Frobenius in the successive reductions of A modulo primes appears to be equidistributed with respect to this distribution. If g = 2, we provide expressions for the cha...

## Post-edited  Heuristics for boundedness of ranks of elliptic curves Poonen, Bjorn (Auteur de la Conférence) | CIRM (Editeur )

We present heuristics that suggest that there is a uniform bound on the rank of $E(\mathbb{Q})$ as $E$ varies over all elliptic curves over $\mathbb{Q}$. This is joint work with Jennifer Park, John Voight, and Melanie Matchett Wood.

## Post-edited  Integral points on Markoff type cubic surfaces and dynamics Sarnak, Peter (Auteur de la Conférence) | CIRM (Editeur )

Cubic surfaces in affine three space tend to have few integral points .However certain cubics such as $x^3 + y^3 + z^3 = m$, may have many such points but very little is known. We discuss these questions for Markoff type surfaces: $x^2 +y^2 +z^2 -x\cdot y\cdot z = m$ for which a (nonlinear) descent allows for a study. Specifically that of a Hasse Principle and strong approximation, together with "class numbers" and their averages for the corresponding nonlinear group of morphims of affine three space. Cubic surfaces in affine three space tend to have few integral points .However certain cubics such as $x^3 + y^3 + z^3 = m$, may have many such points but very little is known. We discuss these questions for Markoff type surfaces: $x^2 +y^2 +z^2 -x\cdot y\cdot z = m$ for which a (nonlinear) descent allows for a study. Specifically that of a Hasse Principle and strong approximation, together with "class numbers" and their averages for the ...

## Multi angle  How to prove that Galois groups are "large" Serre, Jean-Pierre (Auteur de la Conférence) | CIRM (Editeur )

The Galois groups of the title are those which are associated with elliptic curves over number fields; I shall explain the methods which were introduced in the 1960's in order to prove that they are large, and the questions about them which are still open fifty years later.
Galois - elliptic - l-adic - Tate - proofs

## Multi angle  Computing the image of Galois representations attached to elliptic curves Sutherland, Andrew (Auteur de la Conférence) | CIRM (Editeur )

Let $E$ be an elliptic curve over a number field $K$. For each integer $n > 1$ the action of the absolute Galois group $G_K := Gal(\overline{K}/K)$ on the $n$-torsion subgroup $E [n]$ induces a Galois representation $\rho_{E,n}:G_K \rightarrow$ Aut$(E[n]) \backsimeq GL_2(\mathbb{Z} /n\mathbb{Z})$. The representations $\rho_{E,n}$ form a compatible system, and after taking inverse limits one obtains an adelic representation $\rho_E:G_K \rightarrow GL_2(\hat{\mathbb{Z}})$. If $E/K$ does not have $CM$, then Serre's open image theorem implies that the image of $\rho_E$ has finite index in $GL_2(\hat{\mathbb{Z}})$; in particular, $\rho_{E,\ell}$ is surjective for all but finitely many primes $\ell$.
I will present an algorithm that, given an elliptic curve $E/K$ without $CM$, determines the image of $\rho_{E,\ell}$ in $GL_2(\mathbb{Z} /\ell\mathbb{Z})$ up to local conjugacy for every prime $\ell$ for which $\rho_{E,\ell}$ is non-surjective. Assuming the generalized Riemann hypothesis, the algorithm runs in time that is polynomial in the bit-size of the coefficients of an integral Weierstrass model for $E$. I will then describe a probabilistic algorithm that uses this information to compute the index of $\rho_E$ in $GL_2(\hat{\mathbb{Z}})$.

## Single angle  Distributions of Frobenius of elliptic curves #2 David, Chantal (Auteur de la Conférence) | CIRM (Editeur )

In all the following, let an elliptic curve $E$ defined over $\mathbb{Q}$ without complex multiplication. For every prime $\ell$, let $E[\ell]= E[\ell](\overline{\mathbb{Q}})$ be the group of  $\ell$-torsion points of  $E$, and let $K_\ell$  be the field extension obtained from $\mathbb{Q}$ by adding the coordinates of the $\ell$-torsion points of $E$. This is a Galois extension of$\mathbb{Q}$ , andGal$(K_\ell/\mathbb{Q})\subseteq GL_2(\mathbb{Z}/\ell\mathbb{Z})$.
Using the Chebotarev density theorem for the extensions $K_\ell/\mathbb{Q}$ associated to a given curve $E$, we can study various sequences associated to the reductions of a global curve $E/(\mathbb{Q}$, as the sequences
$\left \{\#E(\mathbb{F}_p)=p+1-a_p(E)\right \}_{p\: primes}, or \left \{ a_p(E)=r \right \}_{p\: primes}$
for some fixed value $r\in \mathbb{Z}$. For example, if  $\pi_{E,r}(x)= \#\left \{ p\leq x : a_p(E)=r \right \}$,
then it was shown by Serre and K. Murty, R. Murty and Saradha that under the GRH,
$\pi_{E,r}(x)\ll x^{4/5} log^{-1/5}x$, for all $r\in \mathbb{Z}$, and $\pi_{E,0}(x)\ll x^{3/4}$.
There are also some weaker bounds without the GRH. Some other sequences may also be treated by apply-ing the Chebotarev density theorem to other extensions of $\mathbb{Q}$ as the ones coming from the "mixed Galois representations" associated to $E[\ell]$ and a given quadratic field $K$  which can be used to get upper bounds onthe number of primes $p$ such that End $(E/\mathbb{F}_p)\bigotimes \mathbb{Q}$  is isomorphic to a given quadratic imaginary field $K$ .
We will also explain how the densities obtained from the Cheboratev density theorem can be used togetherwith sieve techniques. For a first application, we consider a conjecture of Koblitz which predicts that
$\pi_{E}^{twin}(x):=\#\left \{ p\leq x : p+1-a_p(E)\, is\, prime \right \}\sim C_{E}^{twin}\frac{x}{log^2x}$
This is analogue to the classical twin prime conjecture, and the constant $C_{E}^{twin}$  can be explicitly writtenas an Euler product like the twin prime constant. We explain how classical sieve techniques can be usedto show that under the GRH, there are at least 2.778 $C_{E}^{twin}x/log^2x$ primes $p$ such that $p+1-a_p(E)^2$ has at most 8 prime factors, counted with multiplicity. We also explain some possible generalisation of Koblitz conjectures which could be treated by similar techniques given some explicitversions (i.e. with explicit error terms) of density theorems existing in the literature.
Other examples of sieving using the Chebotarev density theorem in the context of elliptic curves are thegeneralisations of Hooley's proof of the Artin's conjecture on primitive roots (again under the GRH).Using a similar techniques, but replacing the cyclotomic fields by the $\ell$-division fields $K_\ell$  of a given elliptic curve $E/\mathbb{Q}$, Serre showed that there is a positive proportion of primes $p$ such that the group $E(\mathbb{F}_p)$ is cyclic (when $E$ does not have a rational 2-torsion point). This was generalised by Cojocaru and Duke, and is also related to counting square-free elements of the sequence $a_p(E)^2-4p$,,which still resists a proof with the same techniques (without assuming results stronger than the GRH).
Finally, we also discuss some new distribution questions related to elliptic curves that are very similar to the questions that could be attacked with the Chebotarev density theorem, but are still completely open(for example, no non-trivial upper bounds exists). The first question was first considered by Silverman and Stange who defined an amicable pair of an elliptic curve $E/\mathbb{Q}$  to be a pair of primes $(p,q)$ such that
$p+1-a_p(E)=q$, and $q+1-a_q(E)=p$.
They predicted that the number of such pairs should be about $\sqrt{x}/log^2x$ for elliptic curves without complex multiplication. A precise conjecture with an explicit asymptotic was made by Jones, who also provided numerical evidence for his conjecture. Among the few results existing in the literature for thisquestion is the work of Parks who gave an upper bound of the correct order of magnitude for the average number (averaging over all elliptic curves) of amicable pairs (and aliquot cycles which are cycles of length $L$). But a non-trivial upper bound for a single elliptic curve is still not known.
Another completely open question is related to "champion primes", which are primes $p$ such that $\#E(\mathbb{F}_p)$ is maximal, i.e. $a_p(E)=-[2\sqrt{p}]$. (This terminology was used for the first time by Hedetniemi, James andXue). In some work in progress with Wu, we make a conjecture and give some evidence for the number of champion primes associated to a given elliptic curve using the Sato-Tate conjecture (for verysmall intervals depending on $p$ i.e. in a range where the conjecture is still open). Again, this question iscompletely open, and there are no known non-trivial upper bound. There is also no numerical evidence for this question, and it would be nice to have some, possibly for more general "champion primes", for examplelooking at $a_p(E)$ in a small interval of length $p^\varepsilon$ around $-[2\sqrt{p}]$.
In all the following, let an elliptic curve $E$ defined over $\mathbb{Q}$ without complex multiplication. For every prime $\ell$, let $E[\ell]= E[\ell](\overline{\mathbb{Q}})$ be the group of  $\ell$-torsion points of  $E$, and let $K_\ell$  be the field extension obtained from $\mathbb{Q}$ by adding the coordinates of the $\ell$-torsion points of $E$. This is a Galois extension of$\mathbb{Q}$ , andGal$(K_\ell/\mathbb{Q})\subseteq GL_2... ## Single angle Distributions of Frobenius of elliptic curves #5 David, Chantal (Auteur de la Conférence) | CIRM (Editeur ) In all the following, let an elliptic curve$E$defined over$\mathbb{Q}$without complex multiplication. For every prime$\ell$, let$E[\ell]= E[\ell](\overline{\mathbb{Q}})$be the group of$\ell$-torsion points of$E$, and let$K_\ell$be the field extension obtained from$\mathbb{Q}$by adding the coordinates of the$\ell$-torsion points of$E $. This is a Galois extension of$\mathbb{Q}$, andGal$(K_\ell/\mathbb{Q})\subseteq GL_2(\mathbb{Z}/\ell\mathbb{Z})$. Using the Chebotarev density theorem for the extensions$K_\ell/\mathbb{Q}$associated to a given curve$E$, we can study various sequences associated to the reductions of a global curve$E/(\mathbb{Q}$, as the sequences$\left \{\#E(\mathbb{F}_p)=p+1-a_p(E)\right \}_{p\: primes}, or \left \{ a_p(E)=r \right \}_{p\: primes}$for some fixed value$r\in \mathbb{Z}$. For example, if$\pi_{E,r}(x)= \#\left \{ p\leq x : a_p(E)=r \right \}$, then it was shown by Serre and K. Murty, R. Murty and Saradha that under the GRH,$\pi_{E,r}(x)\ll x^{4/5} log^{-1/5}x$, for all$r\in \mathbb{Z}$, and$ \pi_{E,0}(x)\ll x^{3/4}$. There are also some weaker bounds without the GRH. Some other sequences may also be treated by apply-ing the Chebotarev density theorem to other extensions of$\mathbb{Q} $as the ones coming from the "mixed Galois representations" associated to$E[\ell]$and a given quadratic field$K$which can be used to get upper bounds onthe number of primes$p$such that End$(E/\mathbb{F}_p)\bigotimes \mathbb{Q}$is isomorphic to a given quadratic imaginary field$K$. We will also explain how the densities obtained from the Cheboratev density theorem can be used togetherwith sieve techniques. For a first application, we consider a conjecture of Koblitz which predicts that$\pi_{E}^{twin}(x):=\#\left \{ p\leq x : p+1-a_p(E)\, is\, prime \right \}\sim C_{E}^{twin}\frac{x}{log^2x}$This is analogue to the classical twin prime conjecture, and the constant$C_{E}^{twin}$can be explicitly writtenas an Euler product like the twin prime constant. We explain how classical sieve techniques can be usedto show that under the GRH, there are at least 2.778$C_{E}^{twin}x/log^2x$primes$p$such that$p+1-a_p(E)^2$has at most 8 prime factors, counted with multiplicity. We also explain some possible generalisation of Koblitz conjectures which could be treated by similar techniques given some explicitversions (i.e. with explicit error terms) of density theorems existing in the literature. Other examples of sieving using the Chebotarev density theorem in the context of elliptic curves are thegeneralisations of Hooley's proof of the Artin's conjecture on primitive roots (again under the GRH).Using a similar techniques, but replacing the cyclotomic fields by the$\ell$-division fields$K_\ell$of a given elliptic curve$E/\mathbb{Q}$, Serre showed that there is a positive proportion of primes$p$such that the group$E(\mathbb{F}_p)$is cyclic (when$E$does not have a rational 2-torsion point). This was generalised by Cojocaru and Duke, and is also related to counting square-free elements of the sequence$a_p(E)^2-4p$,,which still resists a proof with the same techniques (without assuming results stronger than the GRH). Finally, we also discuss some new distribution questions related to elliptic curves that are very similar to the questions that could be attacked with the Chebotarev density theorem, but are still completely open(for example, no non-trivial upper bounds exists). The first question was first considered by Silverman and Stange who defined an amicable pair of an elliptic curve$E/\mathbb{Q}$to be a pair of primes$(p,q)$such that$p+1-a_p(E)=q$, and$q+1-a_q(E)=p$. They predicted that the number of such pairs should be about$\sqrt{x}/log^2x$for elliptic curves without complex multiplication. A precise conjecture with an explicit asymptotic was made by Jones, who also provided numerical evidence for his conjecture. Among the few results existing in the literature for thisquestion is the work of Parks who gave an upper bound of the correct order of magnitude for the average number (averaging over all elliptic curves) of amicable pairs (and aliquot cycles which are cycles of length$L$). But a non-trivial upper bound for a single elliptic curve is still not known. Another completely open question is related to "champion primes", which are primes$p$such that$\#E(\mathbb{F}_p)$is maximal, i.e.$a_p(E)=-[2\sqrt{p}]$. (This terminology was used for the first time by Hedetniemi, James andXue). In some work in progress with Wu, we make a conjecture and give some evidence for the number of champion primes associated to a given elliptic curve using the Sato-Tate conjecture (for verysmall intervals depending on$p$i.e. in a range where the conjecture is still open). Again, this question iscompletely open, and there are no known non-trivial upper bound. There is also no numerical evidence for this question, and it would be nice to have some, possibly for more general "champion primes", for examplelooking at$a_p(E)$in a small interval of length$p^\varepsilon$around$-[2\sqrt{p}]$. In all the following, let an elliptic curve$E$defined over$\mathbb{Q}$without complex multiplication. For every prime$\ell$, let$E[\ell]= E[\ell](\overline{\mathbb{Q}})$be the group of$\ell$-torsion points of$E$, and let$K_\ell$be the field extension obtained from$\mathbb{Q}$by adding the coordinates of the$\ell$-torsion points of$E $. This is a Galois extension of$\mathbb{Q}$, andGal$(K_\ell/\mathbb{Q})\subseteq GL_2...

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