Hung–Tiep's conductor-degree conjecture for character fields

Let GG be a finite group and let χ\chi be an irreducible complex character of GG. Let Q(χ)\mathbb{Q}(\chi) be the field generated by the values of χ\chi, and let c(χ)c(\chi) be the smallest positive integer such that Q(χ)⊆Qc(χ)\mathbb{Q}(\chi)\subseteq\mathbb{Q}_{c(\chi)}, where Qn\mathbb{Q}_n is the field generated by a primitive nnth root of unity. Hung–Tiep's conjecture. One has

∣Qc(χ):Q(χ)∣≤χ(1).|\mathbb{Q}_{c(\chi)}: \mathbb{Q}(\chi)| \leq \chi(1).

Hung and Tiep verified this for alternating, unitary, and general linear groups, and whenever χ(1)≤3\chi(1)\leq 3; Hung, Tiep, and Zalesski verified it when χ(1)\chi(1) is prime. The general case is presented here as a conjecture, although the paper's abstract states that the corresponding question is answered negatively at the element level.

References

Primary source

Christopher Herbig, “Answer to a Question of Hung and Tiep on Conductors of Cyclotomic Integers”, arXiv:2508.16732 (2025).

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