Abstract
We show that the Hopf algebra of quasisymmetric functions arises naturally as the integral Chow ring of the algebraic stack of expanded pairs originally described by J. Li, using a more combinatorial description in terms of configurations of line bundles. In particular, we exhibit a gluing map which gives rise to the comultiplication. We then apply the result to calculate the Chow rings of certain stacks of semistable curves.
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Notes
I.e., isomorphic to a polynomial algebra.
All \(M_I\) for \(\ell (I) > \vert \mathfrak {I}\vert \) are identically 0.
The proof given in [4] is for schemes, but will work unchanged for stacks as a base if the vector bundle is trivial.
In the topological setting, we have \(BU(1) = {{\mathbb {C}}}{{\mathbb {P}}}^\infty \). In this spirit, one could regard \(B{{\mathbb {G}}}_m\) as an algebraic version of \({{\mathbb {P}}}^\infty \).
Except over the empty set.
The symbol “nr” stands for “non-rigid.”
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Oesinghaus, J. Quasisymmetric functions and the Chow ring of the stack of expanded pairs. Res Math Sci 6, 5 (2019). https://doi.org/10.1007/s40687-018-0168-7
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DOI: https://doi.org/10.1007/s40687-018-0168-7