Euler system

In mathematics, an Euler system is collection of compatible elements of Galois cohomology groups indexed by fields. They were introduced by Kolyvagin (1990) in his work on Heegner points on modular elliptic curves, which was motivated by his earlier paper Kolyvagin (1988) and the work of Thaine (1988). Euler systems are named after Leonhard Euler because the factors relating different elements of an Euler system resemble the Euler factors of an Euler product.

Euler systems can be used to construct annihilators of ideal class groups or Selmer groups, thus giving bounds on their orders, which in turn has led to deep theorems such as the finiteness of some Tate-Shafarevich groups. This led to Karl Rubin's new proof of the main conjecture of Iwasawa theory, considered simpler than the original proof due to Barry Mazur and Andrew Wiles.

1 Definition
2 Examples
3 Notes
4 References
5 External links

Definition

Although there are several definitions of special sorts of Euler system, there seems to be no published definition of an Euler system that covers all known cases. But it is possible to say roughly what an Euler system is, as follows:

An Euler system is given by collection of elements c_F. These elements are often indexed by certain number fields F containing some fixed number field K, or by something closely related such as square-free integers. The elements c_F are typically elements of some Galois cohomology group such as H¹(F, T) where T is a p-adic representation of the absolute Galois group of K.
The most important condition is that the elements c_F and c_Gfor two different fields F ⊆ G are related by a simple formula, such as

${\rm cor}_{G/F}(c_G) = \prod_{q\in \Sigma(G/F)}P(F_q^{-1}|{\rm Hom}_O(T,O(1));F_q^{-1})c_F$

Here the "Euler factor" P(τ|B;x) is defined to be the element det(1-τx|B) considered as an element of O[x], which when x happens to act on B is not the same as det(1-τx|B) considered as an element of O.

There may be other conditions that the c_F have to satisfy, such as congruence conditions.

Kazuya Kato refers to the elements in an Euler system as "arithmetic incarnations of zeta" and describes the property of being an Euler system as "an arithmetic reflection of the fact that these incarnations are related to special values of Euler products".^[1]

Examples

Cyclotomic units

For every square-free positive integer n pick an n-th root ζ_n of 1, with ζ_mn = ζ_mζ_n for m,n coprime. Then the cyclotomic Euler system is the set of numbers α_n = 1 − ζ_n. These satisfy the relations

$N_{Q(\zeta_{nl})/Q(\zeta_l)}(\alpha_{nl}) = \alpha_n^{F_l-1}$

$\alpha_{nl}\equiv\alpha_n$ modulo all primes above l

where l is a prime not dividing n and F_l is a Frobenius automorphism with F_l(ζ_n) = ζl
n. Kolyvagin used this Euler system to give an elementary proof of the Gras conjecture.

Gauss sums

Elliptic units

Heegner points

Kolyvagin constructed an Euler system from the Heegner points of an elliptic curve, and used this to show that in some cases the Tate-Shafarevich group is finite.

Kato's Euler system

Kato's Euler system consists of certain elements occurring in the algebraic K-theory of modular curves. These elements—named Beilinson elements after Alexander Beilinson who introduced them in Beilinson (1984)—were used by Kazuya Kato in Kato (2004) to prove one divisibility in Barry Mazur's main conjecture of Iwasawa theory for elliptic curves.^[2]

Notes

^ Kato 2007, §2.5.1
^ Kato 2007

References

Banaszak, Grzegorz (2001), "Euler systems for number fields", in Hazewinkel, Michiel, Encyclopedia of Mathematics, Springer, ISBN 978-1556080104, http://www.encyclopediaofmath.org/index.php?title=e/e120240
Beilinson, Alexander (1984), "Higher regulators and values of L-functions", in R. V. Gamkrelidze (in Russian), Current problems in mathematics, 24, pp. 181–238, MR 0760999
Kato, Kazuya (2004), "p-adic Hodge theory and values of zeta functions of modular forms", in Pierre Berthelot, Jean-Marc Fontaine, Luc Illusie, Kazuya Kato, and Michael Rapoport, Cohomologies p-adiques et applications arithmétiques. III., Astérisque, 295, Paris: Société Mathématique de France, pp. 117–290, MR 2104361
Kato, Kazuya (2007), "Iwasawa theory and generalizations", in Marta Sanz-Solé, Javier Soria, Juan Luis Varona, and Joan Verdera, International Congress of Mathematicians, I, Zürich: European Mathematical Society, pp. 335–357, MR 2334196, http://www.icm2006.org/proceedings/Vol_I/18.pdf, retrieved 2010-08-12 . Proceedings of the congress held in Madrid, August 22–30, 2006
Kolyvagin, V. A. (1988), "The Mordell-Weil and Shafarevich-Tate groups for Weil elliptic curves", Izvestiya Akademii Nauk SSSR. Seriya Matematicheskaya 52 (6): 1154–1180, ISSN 0373-2436, MR 984214
Kolyvagin, V. A. (1990), "Euler systems", The Grothendieck Festschrift, Vol. II, Progr. Math., 87, Boston, MA: Birkhäuser Boston, pp. 435–483, doi:10.1007/978-0-8176-4575-5_11, ISBN 978-0-8176-3428-5, MR 1106906
Mazur, Barry; Rubin, Karl (2004), "Kolyvagin systems", Memoirs of the American Mathematical Society 168 (799): viii+96, ISBN 978-0-8218-3512-8, ISSN 0065-9266, MR 2031496, http://math.stanford.edu/~rubin/preprints/kolysys.pdf
Rubin, Karl (2000), Euler systems, Annals of Mathematics Studies, 147, Princeton University Press, MR 1749177, http://books.google.com/books?isbn=0691050767
Scholl, A. J. (1998), "An introduction to Kato's Euler systems", Galois representations in arithmetic algebraic geometry (Durham, 1996), London Math. Soc. Lecture Note Ser., 254, Cambridge University Press, pp. 379–460, ISBN 978-0-521-64419-8, MR 1696501, http://books.google.com/books?isbn=9780521644198
Thaine, Francisco (1988), "On the ideal class groups of real abelian number fields", Annals of Mathematics. Second Series 128 (1): 1–18, doi:10.2307/1971460, ISSN 0003-486X, MR 951505

External links

Several papers on Kolyvagin systems are available at Barry Mazur's web page (as of July 2005).

L-functions in number theory

Analytic examples	Riemann zeta function • Dirichlet L-functions • L-functions of Hecke characters • Automorphic L-functions • Selberg class

Algebraic examples	Dedekind zeta functions • Artin L-functions • Hasse–Weil L-functions • Motivic L-functions

Theorems	Analytic class number formula • Weil conjectures

Analytic conjectures	Riemann hypothesis • Generalized Riemann hypothesis • Lindelöf hypothesis • Ramanujan–Petersson conjecture • Artin conjecture

Algebraic conjectures	Birch and Swinnerton-Dyer conjecture • Deligne's conjecture • Beilinson conjectures • Bloch–Kato conjecture • Langlands conjecture

p-adic L-functions	Main conjecture of Iwasawa theory • Selmer group • Euler system