Papers › The local-global conjecture for Apollonian circle packings is false

The local-global conjecture for Apollonian circle packings is false

6 Jul 2023arXiv:2307.02749links table onlyarchive 2025-07-28

Summer Haag, Clyde Kertzer, James Rickards, Katherine E. Stange

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In a primitive integral Apollonian circle packing, the curvatures that appear must fall into one of six or eight residue classes modulo 24. The local-global conjecture states that every sufficiently large integer in one of these residue classes will appear as a curvature in the packing. We prove that this conjecture is false for many packings, by proving that certain quadratic and quartic families are missed. The new obstructions are a property of the thin Apollonian group (and not its Zariski closure), and are a result of quadratic and quartic reciprocity, reminiscent of a Brauer-Manin obstruction. Based on computational evidence, we formulate a new conjecture.

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