Let be an algebraic group over a field . As defined by Serre, a cohomological invariant of of degree with values in is a functorial-in- collection of maps of sets for all field extensions , where is the set of isomorphism classes of -torsors over Spec . We study the group of degree invariants of an algebraic torus with values in . In particular, we compute the group of unramified cohomology of an algebraic torus .
Sam Blinstein. Alexander Merkurjev. "Cohomological invariants of algebraic tori." Algebra Number Theory 7 (7) 1643 - 1684, 2013. https://doi.org/10.2140/ant.2013.7.1643