p-adic integration and elliptic curves over number fields p-adic Methods in Number Theory, Milano Xavier Guitart 1 Marc Masdeu 2 Mehmet Haluk Sengun 3 1 Institut f ¨ ur Experimentelle Mathematik 2 University of Warwick 3 Sheffield University October 22, 2014 Marc Masdeu p-adic integration and elliptic curves October 22, 2014 0 / 22
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p-adic integration and elliptic curves over number fields
Slides of the talk given at Milano in October 2014.
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p-adic integration and elliptic curvesover number fields
p-adic Methods in Number Theory, Milano
Xavier Guitart 1 Marc Masdeu 2 Mehmet Haluk Sengun 3
1Institut fur Experimentelle Mathematik
2University of Warwick
3Sheffield University
October 22, 2014
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 0 / 22
The Machine
Darmon Points
E/F K/F quadratic
P?∈ E(Kab)
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 1 / 22
The Machine
Non-archimedean
Archimedean
Ramification
Darmon Points
H∗ H∗
Modularity
E/F
K/F quadratic
P?∈ E(Kab)
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 1 / 22
The Machine
Non-archimedean
Archimedean
Ramification
Darmon Points
H∗ H∗
K/F quadratic
P?∈ Ef (Kab)
f ∈ S2(Γ0(N))
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 1 / 22
The Machine
Non-archimedean
Archimedean
Ramification
Darmon Points
H∗ H∗
f ∈ S2(Γ0(N))
???
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 1 / 22
Set-up
K a number field.Fix an ideal N Ă OK .Finitely many iso. classes of EK with condpEq “ N:
ProblemGiven N ą 0, find all elliptic curves of conductor N with
|NmKQpNq| ď N.
K “ Q: Tables by J. Cremona (N “ 350, 000).§ W. Stein–M. Watkins: N “ 108 (N “ 1010 for prime N) incomplete.
K “ Qp?
5q: ongoing project, led by W. Stein (N “ 1831, first rank 2).S. Donnelli–P. Gunnells–A. Kluges-Mundt–D. Yasaki:Cubic field of discriminant ´23 (N “ 1187).
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 2 / 22
StrategyTwo steps
1 Find a list of elliptic curves of with conductor of norm ď N .2 “Prove” that the obtained list is complete.
1 For (1) the process is as follows:1 List Weierstrass equations of small height.2 Compute their conductors (Tate’s algorithm).3 Compute isogeny graph of the curves in the list.4 Twist existing curves by small primes to get other curves.
2 For (2) use modularity conjecture:1 condpEKq “ N ùñ D automorphic form of level N.2 Compute the fin. dim. space S2pΓ0pNqq, with its Hecke action.3 Match all rational eigenclasses to curves in the list.
3 In this talk: assume modularity when needed.4 One is left with some gaps: some conductor N for which there exists
automorphic newform with rational eigenvalues taqpfquq.§ Problem: Find the elliptic curve attached to taqpfquq.
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 3 / 22
Goals of the talk
1 Recall the existing analytic constructions of elliptic curves
2 Propose a conjectural p-adic construction
3 Show an example
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 4 / 22
The case K “ Q: Eichler–Shimura
X0pNq Ñ JacpX0pNqq
ş
–H0pX0pNq,Ω
1X0pNq
q_
H1pX0pNq,ZqHecke CΛf .
Theorem (Manin)There is an isogeny
η : CΛf Ñ Ef pCq.
1 Compute H1pΓ0pNq,Zq (modular symbols).2 Find the period lattice Λf by explicitly integrating
Λf “
C
ż
γ2πi
ÿ
ně1
anpfqe2πinz : γ P H1pX0pNq,Zq
G
.
3 Compute c4pΛf q, c6pΛf q P C by evaluating Eistenstein series.4 Recognize c4pΛf q, c6pΛf q as integers ; Ef : Y 2 “ X3 ´ c4
48X ´c6
864 .
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 5 / 22
K ‰ Q. Existing constructionsK totally real. rK : Qs “ n, fix σ : K ãÑ R.
S2pΓ0pNqq Q f ; ωf P HnpX0pNq,Cq; Λf Ď C.
Conjecture (Oda, Darmon, Gartner)CΛf is isogenous to Ef bK Kσ.
Known to hold (when F real quadratic) for base-change of EQ.Exploited in very restricted cases (Dembele, . . . ).Explicitly computing Λf is hard –no quaternionic computations–.
K not totally real: no known algorithms. In fact:
TheoremIf K is imaginary quadratic, the lattice Λf is contained in R.
IdeaTry instead a non-archimedean construction!
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 6 / 22
Non-archimedean construction
From now on: assume there is some p such that p ‖ N.Replace the role of R (and C) with Kp (and its extensions).
Theorem (Tate uniformization)Let EK be an elliptic curve of conductor N, and let p ‖ N. There exists arigid-analytic, Galois-equivariant isomorphism
η : Kˆp ΛE Ñ EpKpq,
where ΛE “ qZE , with qE P Kp satisfyingjpEq “ q´1
E ` 744` 196884qE ` ¨ ¨ ¨ .
Suppose D coprime factorization N “ pDm, with D “ discpBKq.§ Always possible when K has at least one real place.
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 7 / 22
Quaternionic modular forms of level NSuppose K has signature pr, sq, and fix N “ pDm.BK the quaternion algebra such that
RampBq “ tq : q | Du Y tvn`1, . . . , vru, pn ď rq.
Known when K “ Q (Darmon, Dasgupta–Greenberg,Longo–Rotger–Vigni), open in general.
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 15 / 22
Lattice: explicit construction
Start f P Hn`spΓD0 ppm,Zqq.
Duality yields f P Hn`spΓD0 ppm,Zqq.
Mayer–Vietoris exact sequence for Γ “ ΓD0 pmq ‹ΓD
0 ppmqΓD
0 pmq:
¨ ¨ ¨ Ñ Hn`s`1pΓ,Zqδ1Ñ Hn`spΓ
D0 ppmq,Zq
βÑ Hn`spΓ
D0 pmq,Zq2 Ñ ¨ ¨ ¨
f new at p ùñ βpfq “ 0.§ f “ δ1pcf q, for some cf P Hn`s`1pΓ,Zq.
ConjectureThe element
Lf “ż
δpcf qωf .
is a nonzero multiple of LppEq.
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 16 / 22
Algorithms
Only when n` s ď 1.
Use explicit presentation for ΓD0 ppmq and ΓD
0 pmq.§ s “ 0 ùñ J. Voight.§ s “ 1 ùñ A. Page.
Compute the Hecke action on H1pΓD0 ppm,Zqq and H1pΓ
D0 ppm,Zqq.
Integration pairing uses overconvergent cohomology.§ Lift f to overconvergent class F P Hn`spΓD
0 ppmq,Dq.§ Use F to to recover moments the measures ωf pγq.
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 17 / 22
Overconvergent Method (I)Starting data: cohomology class Φ “ ωf P H
1pΓ,Ω1Hpq.
Goal: to compute integralsşτ2τ1
Φγ , for γ P Γ.Recall that
ż τ2
τ1
Φγ “
ż
P1pKpq
logp
ˆ
t´ τ1
t´ τ2
˙
dµγptq.
Expand the integrand into power series and change variables.§ We are reduced to calculating the moments:
ż
Zp
tidµγptq for all γ P Γ.
Note: Γ Ě ΓD0 pmq Ě ΓD
0 ppmq.Technical lemma: All these integrals can be recovered from#
ż
Zp
tidµγptq : γ P ΓD0 ppmq
+
.
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 18 / 22
Overconvergent Method (II)
D “ tlocally analytic Zp-valued distributions on Zpu.§ ϕ P D maps a locally-analytic function h on Zp to ϕphq P Zp.§ D is naturally a ΓD
0 ppmq-module.
The map ϕ ÞÑ ϕp1Zpq induces a projection:
ρ : H1pΓD0 ppmq,Dq Ñ H1pΓD
0 ppmq,Zpq.
Theorem (Pollack-Stevens, Pollack-Pollack)There exists a unique Up-eigenclass F lifting f .
Moreover, F is explicitly computable by iterating the Up-operator.
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 19 / 22
Overconvergent Method (III)
But we wanted to compute the moments of a system of measures. . .
PropositionConsider the map G : ΓD
0 ppmq Ñ D:
γ ÞÑ”
hptq ÞÑ
ż
Zp
hptqdµγptqı
.
1 G belongs to H1pΓD0 ppmq,Dq.
2 G is a lift of f .3 G is a Up-eigenclass.
CorollaryThe explicitly computed F knows the above integrals.
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 20 / 22
Recovering E from Lf
Start with q “ log´1p pLf q P Cˆp , assume ordppqq ą 0.
Getjpqq “ q´1 ` 744` 196884q ` ¨ ¨ ¨ P Cˆp .
From N guess the discriminant ∆E .§ Only finitely-many possibilities, ∆E P SpK, 12q.
From j “ c34∆ recover c4 P Cp.
Try to recognize c4 algebraically.From 1728∆ “ c3
4 ´ c26 recover c6.
Compute the conductor of Ef : Y 2 “ X3 ´ c448X ´
c6864 .
§ If conductor is correct, check ap’s.
Marc Masdeu p-adic integration and elliptic curves October 22, 2014 21 / 22
Example curveK “ Qpαq, pαpxq “ x4 ´ x3 ` 3x´ 1, ∆K “ ´1732.N “ pα´ 2q “ P13.BK of ramified only at all infinite real places of K.There is a rational eigenclass f P S2pΓ0p1,Nqq.From f we compute ωf P H1pΓ,Ω1