Torsion conjecture

For the definition of uniformly bounded functions, see [[:Uniform boundedness]]. For the result in functional analysis, see [[:Uniform boundedness principle]].

In algebraic geometry and number theory, the torsion conjecture or uniform boundedness conjecture 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.

Elliptic curves

Torsion conjecture for elliptic curves

Field	Number theory
Conjectured by	Andrew Ogg
Conjectured in	1973
First proof by	Barry Mazur Sheldon Kamienny Loïc Merel
First proof in	1977–1996

The (strong) torsion conjecture first posed by Ogg (1973) has been completely resolved in the case of elliptic curves. Barry Mazur (1977, 1978) proved uniform boundedness for elliptic curves over the rationals. His techniques were generalized by Kamienny (1992) and Kamienny & Mazur (1995), who obtained uniform boundedness for quadratic fields and number fields of degree at most 8 respectively. Finally, Loïc Merel (1996) proved the conjecture for elliptic curves over any number field. The proof centers around a careful study of the rational points on classical modular curves. An effective bound for the size of the torsion group in terms of the degree of the number field was given by Parent (1999).

Mazur provided a complete list of possible torsion subgroups for rational elliptic curves. If C_n denotes the cyclic group of order n, then the possible torsion subgroups are C_n with 1 ≤ n ≤ 10, and also C₁₂; and the direct sum of C₂ with C₂, C₄, C₆ or C₈. In the opposite direction, all these torsion structures occur infinitely often over Q, since the corresponding modular curves are all genus zero curves with a rational point. A complete list of possible torsion groups is also available for elliptic curves over quadratic number fields. A complete list for cubic number fields has been claimed in (a recent preprint 2020) and there are substantial partial results for quartic and quintic number fields (Sutherland 2012).

References

• Kamienny, Sheldon (1992). "Torsion points on elliptic curves and $q$-coefficients of modular forms". Inventiones Mathematicae. 109 (2): 221–229. Bibcode:1992InMat.109..221K. doi:10.1007/BF01232025. MR 1172689. {{cite journal}}: Invalid |ref=harv (help)
• Kamienny, Sheldon; Mazur, Barry (1995). "Rational torsion of prime order in elliptic curves over number fields". Astérisque. 228. With an appendix by A. Granville: 81–100. MR 1330929. {{cite journal}}: Invalid |ref=harv (help)
• Mazur, Barry (1977). "Modular curves and the Eisenstein ideal". Publications Mathématiques de l'IHÉS. 47 (1): 33–186. doi:10.1007/BF02684339. MR 0488287. {{cite journal}}: Invalid |ref=harv (help)
• Mazur, Barry (1978), "Rational isogenies of prime degree", Inventiones Mathematicae, 44 (2), with appendix by Dorian Goldfeld: 129–162, Bibcode:1978InMat..44..129M, doi:10.1007/BF01390348, MR 0482230 {{citation}}: Invalid |ref=harv (help)
• Merel, Loïc (1996). "Bornes pour la torsion des courbes elliptiques sur les corps de nombres" [Bounds for the torsion of elliptic curves over number fields]. Inventiones Mathematicae (in French). 124 (1): 437–449. Bibcode:1996InMat.124..437M. doi:10.1007/s002220050059. MR 1369424. {{cite journal}}: Invalid |ref=harv (help)
• Ogg, Andrew (1973). "Rational points on certain elliptic modular curves". Proc. Symp. Pure Math. Proceedings of Symposia in Pure Mathematics. 24: 221–231. doi:10.1090/pspum/024/0337974. ISBN 9780821814246.
• Parent, Pierre (1999). "Bornes effectives pour la torsion des courbes elliptiques sur les corps de nombres" [Effective bounds for the torsion of elliptic curves over number fields]. Journal für die Reine und Angewandte Mathematik (in French). 1999 (506): 85–116. arXiv:alg-geom/9611022. doi:10.1515/crll.1999.009. MR 1665681. {{cite journal}}: Invalid |ref=harv (help)
• Sutherland, Andrew V. (2012), Torsion subgroups of elliptic curves over number fields (PDF)
• Derickx, Maarten; Etropolski, Anastasia; van Hoeij, Mark; Morrow, Jackson; Zureick Brown, David (2020), Sporadic Cubic Torsion