Strong uniform boundedness conjecture for Brauer groups of K3 surfaces

Let kk) be a number field with [k:Q]d[k:\mathbb{Q}]\leq d, let LΛL\hookrightarrow\Lambda be a primitive sublattice, and let XX be a K3 surface over kk such that Pic(X)L\operatorname{Pic}(\overline{X})\simeq L. The quotient Br(X)/Br0(X)\operatorname{Br}(X)/\operatorname{Br}_0(X) is finite, where Br0(X)\operatorname{Br}_0(X) is the subgroup of constant algebras.

Strong uniform boundedness conjecture. There is a constant B=B(d,L)B=B(d,L), independent of XX, such that

#Br(X)Br0(X)<B.\#\frac{\operatorname{Br}(X)}{\operatorname{Br}_0(X)}<B.

This conjecture predicts uniform boundedness in fixed-degree number fields and fixed geometric Picard lattice. The algebraic quotient Br1(X)/Br0(X)\operatorname{Br}_1(X)/\operatorname{Br}_0(X) is already known to be uniformly bounded, so the substantive issue is the transcendental Brauer group. The source gives no resolution status.

Sources & referencesView supporting material

Primary source

Danny Bragg, Emma Brakkee and Anthony Várilly-Alvarado, “Moduli of lattice-polarized K3 surfaces and boundedness of Brauer groups”, arXiv:2510.11477 (2025).

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