Restricted inverse Galois problem over function fields

Let pp be a prime and let GG be a nontrivial finite group. Write GabG^{ab} for the abelianization of GG, let p(G)p(G) be the normal subgroup generated by the elements of pp-power order, and let

d=d((G/p(G))ab).d=d\left((G/p(G))^{ab}\right).

For the global function field Fp(t)\mathbb{F}_p(t), let RamFp(t)(G)\operatorname{Ram}_{\mathbb{F}_p(t)}(G) denote the minimum number of places ramified in a GG-extension of Fp(t)\mathbb{F}_p(t). Restricted inverse Galois conjecture. There exists a GG-extension of Fp(t)\mathbb{F}_p(t) such that

RamFp(t)(G)={d+1if pGab,max(d,1)if pGab.\operatorname{Ram}_{\mathbb{F}_p(t)}(G)=\begin{cases} d+1 & \text{if } p\mid |G^{ab}|,\\ \max(d,1) & \text{if } p\nmid |G^{ab}|. \end{cases}

This refines the problem of minimizing ramification in geometric Galois extensions of rational function fields, combining the expected contribution from the abelianization with the behavior of the normal subgroup generated by elements of pp-power order. The source presents the statement as a conjecture based on related work and families of examples; its resolution status is not specified here.

Sources & referencesView supporting material

Primary source

Meghan De Witt, “Minimal ramification and the inverse Galois problem over the rational function field F_p(t)”, arXiv:1410.8381 (2014).

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