Torsion conjecture

{{For|other uniform boundedness conjectures|Uniform boundedness conjecture (disambiguation){{!}}Uniform boundedness conjecture}}

In algebraic geometry and number theory, the torsion conjecture or uniform boundedness conjecture for torsion points for abelian varieties states that the order of the torsion group of an abelian variety over a number field can be bounded in terms of the dimension of the variety and the number field. A stronger version of the conjecture is that the torsion is bounded in terms of the dimension of the variety and the degree of the number field. The torsion conjecture has been completely resolved in the case of elliptic curves.

Elliptic curves

{{Infobox mathematical statement

| name = Ogg's conjecture

| image =

| caption =

| field = Number theory

| conjectured by = Beppo Levi

| conjecture date = 1908

| first proof by = Barry Mazur

| first proof date = 1977–1978

| open problem =

| known cases =

| implied by =

| equivalent to =

| generalizations =

| consequences =

}}

From 1906 to 1911, Beppo Levi published a series of papers investigating the possible finite orders of points on elliptic curves over the rationals.{{sfn|Schappacher|Schoof|1996|pp=64–65}} He showed that there are infinitely many elliptic curves over the rationals with the following torsion groups:

C_n with 1 ≤ n ≤ 10, where C_n denotes the cyclic group of order n;
C₁₂;
C_2n × C₂ with 1 ≤ n ≤ 4, where × denotes the direct sum.

At the 1908 International Mathematical Congress in Rome, Levi conjectured that this is a complete list of torsion groups for elliptic curves over the rationals.{{sfn|Schappacher|Schoof|1996|pp=64–65}} The torsion conjecture for elliptic curves over the rationals was independently reformulated by {{harvs|txt|first=Trygve|last=Nagell|author-link=Trygve Nagell|year=1952}} and again by {{harvs|txt|first=Andrew|last=Ogg|authorlink=Andrew Ogg |year=1971}}, with the conjecture becoming commonly known as Ogg's conjecture.{{sfn|Schappacher|Schoof|1996|pp=64–65}}

{{harvs|txt|first=Andrew|last=Ogg|authorlink=Andrew Ogg |year=1971}} drew the connection between the torsion conjecture for elliptic curves over the rationals and the theory of classical modular curves.{{sfn|Schappacher|Schoof|1996|pp=64–65}} In the early 1970s, the work of Gérard Ligozat, Daniel Kubert, Barry Mazur, and John Tate showed that several small values of n do not occur as orders of torsion points on elliptic curves over the rationals.{{sfn|Schappacher|Schoof|1996|pp=64–65}} {{harvs|txt|first=Barry|last=Mazur|authorlink=Barry Mazur|year=1977|year2=1978}} proved the full torsion conjecture for elliptic curves over the rationals. His techniques were generalized by {{harvtxt|Kamienny|1992}} and {{harvtxt|Kamienny|Mazur|1995}}, who obtained uniform boundedness for quadratic fields and number fields of degree at most 8 respectively. Finally, {{harvs|txt|first=Loïc|last=Merel|authorlink=Loïc Merel|year=1996}} proved the conjecture for elliptic curves over any number field.{{sfn|Schappacher|Schoof|1996|pp=64–65}} He proved for {{math|K}} a number field of degree $d=[K:\mathbb{Q}]$ and an elliptic curve $E/K$ that there is a bound on the order of the torsion group depending only on the degree $|E(K)_{\text{tors}}|\leq B(d)$ . Furthermore if $P\in E(K)_{\text{tors}}$ is a point of prime order $p$ we have $p\leq d^{3d^2}.$

An effective bound for the size of the torsion group in terms of the degree of the number field was given by {{harvtxt|Parent|1999}}. Parent proved that for $P\in E(K)_{\text{tors}}$ a point of prime power order $p^n$ we have

$p^n \leq B(d,p)=\begin{cases}
129(3^d-1)(3d)^6&\text{if }p=2,\\
65(5^d-1)(2d)^6&\text{if }p=3,\\
65(3^d-1)(2d)^6&\text{if }p>3.
\end{cases}$

Setting $B_{\text{max}}(d)=129(5^d-1)(3d)^6$ we get from the structure result behind the Mordell-Weil theorem, i.e. there are two integers $n_1,n_2$ such that $E(K)_{\text{tors}}\cong\mathbb{Z}/n_1\mathbb{Z}\times\mathbb{Z}/n_2\mathbb{Z}$ , a coarse but effective bound $B(d)=\left(B_{\text{max}}(d)^{B_{\text{max}}(d)}\right)^2.$

Joseph Oesterlé gave in private notes from 1994 a slightly better bound for points of prime order $p$ of $p\leq (3^{d/2}+1)^2$ , which turns out to be useful for computations over fields of small order, but alone is not enough to yield an effective bound for $|E(K)_{\text{tors}}|$ . {{harvtxt|Derickx|Kamienny|Stein|Stoll|2023}} provide a published version of Oesterlé's result.

For number fields of small degree more refined results are known {{harv|Sutherland|2012}}. A complete list of possible torsion groups has been given for elliptic curves over $\mathbb{Q}$ (see above) and for quadratic and cubic number fields. In degree 1 and 2 all groups that arise occur infinitely often. The same holds for cubic fields except for the group C₂₁ which occurs only in a single elliptic curve over $K=\mathbb{Q}(\zeta_9)^+$ . For quartic and quintic number fields the torsion groups that arise infinitely often have been determined. The following table gives the set of all prime numbers $S(d)$ that actually arise as the order of a torsion point $P\in E(K)_{\text{tors}}$ where $\text{Primes}(q)$ denotes the set of all prime numbers at most q ({{harvtxt|Derickx|Kamienny|Stein|Stoll|2023}} and {{harvtxt|Khawaja|2024}}).

class="wikitable"

|+ Primes that occur as orders of torsion points in small degree $d$

d

S(d)

\text{Primes}(7)

\text{Primes}(13)

\text{Primes}(13)

\text{Primes}(17)

\text{Primes}(19)

\text{Primes}(19)\cup\{37\}

\text{Primes}(23)

\text{Primes}(23)

The next table gives the set of all prime numbers $S'(d)$ that arise infinitely often as the order of a torsion point ({{harvtxt|Derickx|Kamienny|Stein|Stoll|2023}}).

class="wikitable"

|+ Primes that occur infinitely often as orders of torsion points in small degree $d$

d

S'(d)

\text{Primes}(7)

\text{Primes}(13)

\text{Primes}(13)

\text{Primes}(17)

\text{Primes}(19)

\text{Primes}(19)

\text{Primes}(23)

\text{Primes}(23)

Barry Mazur gave a survey talk on the torsion conjecture{{cite arXiv | last1=Balakrishnan | first1=Jennifer S. | author-link1=Jennifer Balakrishnan| last2=Mazur | first2=Barry | last3=Dogra | first3=Netan | title=Ogg's Torsion conjecture: Fifty years later | date=10 July 2023 | eprint=2307.04752 |class=math.NT}} on the occasion of the establishment of the Ogg Professorship{{cite web | title=Frank C. and Florence S. Ogg Professorship Established at IAS | website=Institute for Advanced Study | date=12 October 2022 | url=https://www.ias.edu/news/2022/ogg-professorship-established | access-date=16 April 2024}} at the Institute for Advanced Study in October 2022.

References

Bibliography

{{cite journal | last=Kamienny | first=Sheldon | title=Torsion points on elliptic curves and $q$ -coefficients of modular forms | year=1992 | journal=Inventiones Mathematicae | volume=109 | issue=2 | pages=221–229 | doi=10.1007/BF01232025 | mr=1172689 | bibcode=1992InMat.109..221K | s2cid=118750444 }}
{{cite journal | last1=Kamienny | first1=Sheldon | last2=Mazur | first2=Barry | author2-link=Barry Mazur | title=Rational torsion of prime order in elliptic curves over number fields | others=With an appendix by A. Granville | journal=Astérisque | year=1995 | pages=81–100 | mr=1330929 | volume=228}}
{{cite journal|last=Mazur|first=Barry|author-link=Barry Mazur|title=Modular curves and the Eisenstein ideal|volume=47|issue=1|pages=33–186|year=1977|doi=10.1007/BF02684339|mr=0488287|journal=Publications Mathématiques de l'IHÉS|s2cid=122609075|url=http://www.numdam.org/item/PMIHES_1977__47__33_0/}}
{{citation|last=Mazur|first=Barry|title=Rational isogenies of prime degree|volume=44|issue=2|pages=129–162|year=1978|doi=10.1007/BF01390348|mr=0482230|journal=Inventiones Mathematicae|others=with appendix by Dorian Goldfeld|bibcode=1978InMat..44..129M|s2cid=121987166}}
{{cite journal | last1=Merel | first1=Loïc | author1-link=Loïc Merel | title=Bornes pour la torsion des courbes elliptiques sur les corps de nombres | trans-title=Bounds for the torsion of elliptic curves over number fields | language=fr | doi=10.1007/s002220050059 |mr=1369424 | year=1996 | journal=Inventiones Mathematicae | volume=124 | issue=1 | pages=437–449 | bibcode=1996InMat.124..437M | s2cid=3590991 }}
{{cite book |last=Nagell |first=Trygve |authorlink=Trygve Nagell |chapter=Problems in the theory of exceptional points on plane cubics of genus one |title=Den 11te Skandinaviske Matematikerkongress, Trondheim 1949, Oslo |publisher={{ill|Johan Grundt Tanum forlag|no}} |pages=71–76 |year=1952|oclc=608098404}}
{{cite journal |last=Ogg |first=Andrew |author-link=Andrew Ogg |year=1971 |title=Rational points of finite order on elliptic curves |journal=Inventiones Mathematicae |volume=22 |issue=2 |pages=105–111|doi=10.1007/BF01404654|bibcode=1971InMat..12..105O |s2cid=121794531 }}
{{cite journal|last=Ogg |first=Andrew |author-link=Andrew Ogg |title=Rational points on certain elliptic modular curves|journal=Proc. Symp. Pure Math. |volume=24 |pages=221–231 |year=1973|doi=10.1090/pspum/024/0337974 |series=Proceedings of Symposia in Pure Mathematics |isbn=9780821814246 }}
{{cite journal | last=Parent | first=Pierre | title=Bornes effectives pour la torsion des courbes elliptiques sur les corps de nombres | trans-title=Effective bounds for the torsion of elliptic curves over number fields | language=fr | journal=Journal für die Reine und Angewandte Mathematik | year=1999 | volume=1999 | issue=506 | pages=85–116 | mr=1665681 | doi=10.1515/crll.1999.009 | arxiv=alg-geom/9611022 }}
{{Citation

| last1 = Schappacher

| first1 = Norbert

|authorlink1 = Norbert Schappacher

| last2 = Schoof

| first2 = René

| authorlink2 = René Schoof

| title = Beppo Levi and the arithmetic of elliptic curves

| journal = The Mathematical Intelligencer

| volume = 18

| issue = 1

| pages = 57–69

| year = 1996

| doi = 10.1007/bf03024818

| mr = 1381581

| zbl = 0849.01036

| s2cid = 125072148

| url = http://irma.math.unistra.fr/~schappa/NSch/Publications_files/1996_RSchNSch.pdf

}}

{{cite web | last=Sutherland | first=Andrew V. | title=Torsion subgroups of elliptic curves over number fields | year=2012 | url=https://math.mit.edu/~drew/MazursTheoremSubsequentResults.pdf|website=math.mit.edu }}
{{cite journal|last1=Derickx|first1=Maarten|last2=Kamienny|first2=Sheldon|last3=Stein|first3=William|last4=Stoll|first4=Michael|date=2023|title=Torsion points on elliptic curves over number fields of small degree|journal=Algebra & Number Theory |volume=17 |issue=2 |pages=267–308 |doi=10.2140/ant.2023.17.267 |arxiv=1707.00364}}
{{cite journal|last=Khawaja|first=Maleeha|date=2024|title=Torsion primes for elliptic curves over degree 8 number fields|journal=Research in Number Theory |volume=10 |issue=2 |doi=10.1007/s40993-024-00533-6 |arxiv=2304.14284

}}

Category:Abelian varieties

Category:Conjectures

Category:Diophantine geometry

Category:Theorems in number theory

Category:Theorems in algebraic geometry

Torsion conjecture

Elliptic curves

See also

References

Bibliography