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Motivic classes of some classifying stacks
Stockholm University, Faculty of Science, Department of Mathematics.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We prove that the class of the classifying stack BPGLn is themultiplicative inverse of the class of the projective linear group PGL_nin the Grothendieck ring of stacks K0(Stack_k) for n = 2 and n = 3 under mild conditions on the base field k. In particular, although it is know that the multiplicativity relation {T} = {S}{PGL_n} does not hold for all PGLn-torsors T -> S, it holds for the universal PGLn-torsors for said n.

National Category
Geometry
Research subject
Mathematics
Identifiers
URN: urn:nbn:se:su:diva-107523OAI: oai:DiVA.org:su-107523DiVA: diva2:748046
Available from: 2014-09-18 Created: 2014-09-18 Last updated: 2014-09-18
In thesis
1. Destackification and Motivic Classes of Stacks
Open this publication in new window or tab >>Destackification and Motivic Classes of Stacks
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis consists of three articles treating topics in the theory of algebraic stacks. The first two papers deal with motivic invariants. In the first, we show that the class of the classifying stack BPGLn is the inverse of the class of PGLn in the Grothendieck ring of stacks for n ≤ 3. This shows that the multiplicativity relation holds for the universal torsors, although it is known not to hold for torsors ingeneral for the groups PGL2 and PGL3.

In the second paper, we introduce an exponential function which can be viewed as a generalisation of Kapranov's motivic zeta function. We use this to derive a binomial theorem for a power operation defined on the Grothendieck ring of varieties. As an application, we give an explicit expression for the motivic class of a universal quasi-split torus, which generalises a result by Rökaeus.

The last paper treats destackification. We give an algorithm for removing stackiness from smooth, tame stacks with abelian stabilisers by repeatedly applying stacky blow-ups. As applications, we indicate how the result can be used for destackifying general Deligne–Mumford stacks in characteristic zero, and to obtain a weak factorisation theorem for such stacks.

Place, publisher, year, edition, pages
Stockholm: Department of Mathematics, Stockholm University, 2014. 23 p.
Keyword
Algebraic geometry, Algebraic stacks, Destackification, Grothendieck ring, Motive, Torus, Classifying stack
National Category
Geometry
Research subject
Mathematics
Identifiers
urn:nbn:se:su:diva-107526 (URN)978-91-7447-989-8 (ISBN)
Public defence
2014-10-24, sal 14, hus 5, Kräftriket, Roslagsvägen 101, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript. Paper 3: Manuscript.

Available from: 2014-10-02 Created: 2014-09-18 Last updated: 2014-10-30Bibliographically approved

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