NT Seminar - Katharina Hübner

Mon, 11/11/201914:30-15:30
Ross 70
Title: The tame site
Abstract: For a scheme of characteristic $p > 0$ (or mixed characteristic) \'etale cohomology with $p$-torsion coefficients does not behave very well: Smooth base change, cohomological purity, homotopy invariance, just to name a few, only hold for coefficients prime to the characteristic. The reason for this failure is the existence of wild ramification. This talk presents a modification of the \'etale topology that does not admit for wild ramification, called the tame site. For coefficients away from the characteristic the \'etale and tame cohomology groups are isomorphic and for $p$-torsion coefficients they are better behaved than the \'etale cohomology groups.