The minimal ramification conjecture for finite groups over finite fields

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Let GG be a nontrivial finite group. Write d(G)d(G) for the minimal number of generators of GG, GabG^{\mathrm{ab}} for its abelianization, and p(Gab)p(G^{\mathrm{ab}}) for the subgroup generated by the pp-Sylow subgroups of GabG^{\mathrm{ab}}. An extension of function fields is geometric if the two fields have the same field of constants. Minimal ramification conjecture. There exists a geometric Galois extension K/Fq(T)K/\mathbb{F}_q(T) with

Gal⁡(K/Fq(T))=G\operatorname{Gal}(K/\mathbb{F}_q(T))=G

and ramified over at most rr prime divisors of Fq(T)\mathbb{F}_q(T) if and only if

r≥d(Gab/p(Gab)).r\ge d\left(G^{\mathrm{ab}}/p(G^{\mathrm{ab}})\right).

This conjecture generalizes a corresponding conjecture of Boston and Markin over Q\mathbb{Q} and concerns the minimum number of ramified prime divisors in a finite-group extension. The supplied status evidence says that significant progress is known for the symmetric and alternating groups, but the conjecture remains open for many values of nn and qq.

References

Primary source

Alexei Entin and Noam Pirani, “Abhyankar's Affine Arithmetic Conjecture for the Symmetric and Alternating Groups”, arXiv:2205.03879 (2023).

Additional references

3 papers in this index state this conjecture (2016–2022). The statement above is taken from the most recent of them; the others are arXiv:2106.09126, arXiv:1602.03662.

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