CM residue-disk placement conjecture for supersingular reductions

Let AA be a supersingular elliptic curve defined over Fp\mathbb{F}_p, and let

i=i(A)=Aut(A)/2.i=i(A)=|\operatorname{Aut}(A)|/2.

For a CM elliptic curve E/CpE/\mathbb{C}_p, write Eˉ=A\bar E=A when its reduction is AA, and suppose

pDisc(End(E)).p\mathrel{||}\operatorname{Disc}(\operatorname{End}(E)).

A uniformizer uCpu\in\mathbb{C}_p of the common image and maps λi:EˉiA\lambda_i:\bar E_i\to A are as in the claim.

CM residue-disk placement conjecture. The jj-invariants of all such curves EE lie in 2(p+1)/i2(p+1)/i residue disks inside the corresponding Atkin–Lehner circle, with (p+1)/i(p+1)/i disks for each ramified quadratic extension of Qp\mathbb{Q}_p. Two such curves E1E_1 and E2E_2 lie in the same residue disk if and only if

End(E1)Zp=End(E2)Zp\operatorname{End}(E_1)\otimes\mathbb{Z}_p=\operatorname{End}(E_2)\otimes\mathbb{Z}_p

and

σλ1(u)σλ2(u)Aˉp.\sigma_{\lambda_1}(u)\equiv\sigma_{\lambda_2}(u)\in\bar A_p.

The conjecture is intended to explain the geometric placement of CM jj-invariants and to provide a general theory behind the prime-specific CM placement conjectures at 55, 77, and 1313. The paper states that it has evidence but no proof.

Sources & referencesView supporting material

Primary source

Ken McMurdy, “Stable Model of X_0(125)”, arXiv:math/0403157 (2004).

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