Finiteness conjecture for good quaternionic Shimura levels

Fix an almost indefinite quaternion algebra BB over a totally real number field FF. For an open compact subgroup KK of B×(Af)B^\times(\mathbb A_{\mathrm f}), let XKX_K be the associated Shimura curve; for an open compact subgroup of PB×(Af)PB^\times(\mathbb A_{\mathrm f}), let YKY_K be the corresponding projective Shimura curve. A curve is good if it satisfies the automorphic vanishing criterion for the modified diagonal cycle.

Finiteness conjecture. There are only finitely many open compact subgroups KB×(Af)K\subset B^\times(\mathbb A_{\mathrm f}), respectively KPB×(Af)K\subset PB^\times(\mathbb A_{\mathrm f}), up to conjugation, such that XKX_K, respectively YKY_K, is good and has genus greater than 00.

This fixed-algebra finiteness statement is asserted to imply the broader conjecture on finiteness of good Shimura curves. The paper proves related finiteness results for quaternion algebras, but this level-by-level assertion remains open.

Sources & referencesView supporting material

Primary source

Congling Qiu, “Finiteness properties for Shimura curves and modified diagonal cycles”, arXiv:2310.20600 (2025).

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