Degree and the Brauer–Manin obstruction

Brendan Creutz, Bianca Viray
2018 Algebra & Number Theory  
Let X be a smooth variety over a number field k embedded as a degree d subvariety of P^n and suppose that X is a counterexample to the Hasse principle explained by the Brauer-Manin obstruction. We consider the question of whether the obstruction is given by the d-primary subgroup of the Brauer group, which would have both theoretic and algorithmic implications. We prove that this question has a positive answer in the case of torsors under abelian varieties, Kummer surfaces and (conditional on
more » ... niteness of Tate-Shafarevich groups) bielliptic surfaces. For Kummer varieties we show that the obstruction is already given by the 2-primary torsion. We construct a conic bundle over an elliptic curve that shows that, in general, the answer is no.
doi:10.2140/ant.2018.12.2445 fatcat:sht6yk7jongx5hkuk5flj66hkm