Ramified étale–Brauer obstruction conjecture for stratified varieties

Let kk be a number field and let X/kX/k be a variety with X(k)=X(k)=\emptyset. A stratification of XX is a decomposition

X=iXi.X=\coprod_i X_i.

For each stratum, let \clXi\cl{X_i} be its closure and let YiY_i be a quasi-torsor over \clXi\cl{X_i} that restricts to a torsor over XiX_i; for every twist YiσY_i^{\sigma} of YiY_i, let Yiσ(\Abk)\BrY_i^{\sigma}(\Ab_k)^{\Br} denote its Brauer set. Ramified étale–Brauer obstruction conjecture. There exists such a stratification and, for each ii, such a quasi-torsor YiY_i satisfying

Yiσ(\Abk)\Br=Y_i^{\sigma}(\Ab_k)^{\Br}=\emptyset

for all twists YiσY_i^{\sigma} of YiY_i. This conjecture would show that the absence of rational points is explained by the ramified étale–Brauer obstruction using one quasi-torsor for each stratum.

Sources & referencesView supporting material

Primary source

David Corwin and Tomer Schlank, “Brauer and Etale Homotopy Obstructions to Rational Points on Open Covers”, arXiv:2006.11699 (2020).

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