Grothendieck's section conjecture for hyperbolic curves

Let V/kV/k be a smooth, geometrically connected, hyperbolic curve over a number field kk, with smooth completion VXV\subset X and boundary Y=XVY=X\setminus V. For each kk-rational cusp yY(k)y\in Y(k), let Vy=V×XSpec(OX,yh)V_y=V\times_X\operatorname{Spec}(\mathcal{O}_{X,y}^h) be the scheme of nearby points, and let Sπ1(V/k)\mathscr{S}_{\pi_1(V/k)} denote the set of sections of 1π1(V)π1(V)Galk11\to\pi_1(\overline{V})\to\pi_1(V)\to\operatorname{Gal}_k\to1, considered up to π1(V)\pi_1(\overline{V})-conjugacy. The non-abelian Kummer map is denoted by κ\kappa. Grothendieck's section conjecture. The map

κ:V(k)yY(k)Sπ1(Vy/k)Sπ1(V/k)\kappa: V(k)\sqcup\bigsqcup_{y\in Y(k)}\mathscr{S}_{\pi_1(V_y/k)}\longrightarrow\mathscr{S}_{\pi_1(V/k)}

is bijective. Thus every section is either explained by a unique rational point or belongs to a packet of cuspidal sections based at a unique rational cusp. The conjecture is widely open in this generality: injectivity is known, while surjectivity remains the difficult part. The source notes that the conjecture predicts, in particular, that every Selmer section is rational or cuspidal.

Sources & referencesView supporting material

Primary source

Benjamin Steklov, “Fermat's Last Theorem for Selmer sections”, arXiv:2602.17746 (2026).

Additional references

12 papers in this index state this conjecture (2007–2026). The statement above is taken from the most recent of them; the others are arXiv:2409.07923, arXiv:2407.03248, arXiv:1902.02058, arXiv:1204.1260, arXiv:1111.1354, arXiv:1106.4255, arXiv:0906.0245, arXiv:0902.1653, arXiv:0809.0017, arXiv:0802.4125, arXiv:math/0703877.

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