Eichler–Shimura-type conjecture for weight two eigenforms over number fields

Let KK be a number field, let N\mathfrak N be an ideal of OK\mathcal O_K, and let f\mathfrak f be a non-trivial, new, weight two complex eigenform over KK of level N\mathfrak N. A fake elliptic curve is a simple abelian surface whose algebra of KK-endomorphisms is an indefinite division quaternion algebra over Q\mathbb Q. Eichler–Shimura-type conjecture. If KK has a real place, there exists an elliptic curve Ef/KE_{\mathfrak f}/K of conductor N\mathfrak N such that

#Ef(OK/q)=1+Norm(q)f(Tq)\#E_{\mathfrak f}(\mathcal O_K/\mathfrak q)=1+\operatorname{Norm}(\mathfrak q)-\mathfrak f(T_{\mathfrak q})

for every qN\mathfrak q\nmid\mathfrak N. If KK is totally complex, there exists either such an elliptic curve or a fake elliptic curve Af/KA_{\mathfrak f}/K of conductor N2\mathfrak N^2 satisfying

#Af(OK/q)=(1+Norm(q)f(Tq))2\#A_{\mathfrak f}(\mathcal O_K/\mathfrak q)=(1+\operatorname{Norm}(\mathfrak q)-\mathfrak f(T_{\mathfrak q}))^2

for every qN\mathfrak q\nmid\mathfrak N. This is a special case of a fundamental conjecture from the Langlands programme concerning the connection between eigenforms and elliptic or fake elliptic curves; the source gives no resolution status.

Sources & referencesView supporting material

Primary source

Begum Gulsah Cakti, Erman Isik, Yasemin Kara and Ekin Ozman, “Solving equations of signature (p,p,2) with coefficients over number fields”, arXiv:2602.18871 (2026).

Additional references

23 papers in this index state this conjecture (2007–2026). The statement above is taken from the most recent of them; the others are arXiv:2512.04936, arXiv:2509.21083, arXiv:2509.14280, arXiv:2502.09892, arXiv:2404.07319, arXiv:2404.09171, arXiv:2403.14640, arXiv:2304.09003, arXiv:2301.09263, arXiv:2212.10627, arXiv:2209.09153, arXiv:2207.10930, and 10 more.

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