Abstract
Consider a complex algebraic group G acting on a smooth variety M with finitely many orbits, and let \(\Omega \) be an orbit. The following three invariants of \(\Omega \subset M\) can be characterized axiomatically: (1) the equivariant fundamental class \([\overline{\Omega }, M]\in H^*_G(M)\), (2) the equivariant Chern–Schwartz–MacPherson class \({{\,\mathrm{c^{sm}}\,}}(\Omega , M)\in H^*_G(M)\), and (3) the equivariant motivic Chern class \({{\,\mathrm{mC}\,}}(\Omega , M) \in K_G(M)[y]\). The axioms for Chern–Schwartz–MacPherson and motivic Chern classes are motivated by the axioms for cohomological and K-theoretic stable envelopes of Okounkov and his coauthors. For M a flag variety and \(\Omega \) a Schubert cell—an orbit of the Borel group acting—this implies that CSM and MC classes coincide with the weight functions studied by Rimányi–Tarasov–Varchenko. In this paper we review the general theory and illustrate it with examples.
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Notes
- 1.
Since \(u^k=[\mathcal O_{\mathbb {P}^{n-1-k}}]\in K(\mathbb {P}^{n-1})\) thus \(p_*(u^k)=\chi (\mathbb {P}^{n-1-k};\mathcal O)=1\).
- 2.
This idea appeared already in an early version of [26].
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Acknowledgements
L.F. is supported by NKFI grants K 112735 and KKP 126683. R.R. is supported by the Simon Foundation grant 523882. A.W. is supported by NCN grants 2013/08/A/ST1/00804 and 2016/23/G/ST1/04282.
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Fehér, L.M., Rimányi, R., Weber, A. (2020). Characteristic Classes of Orbit Stratifications, the Axiomatic Approach. In: Hu, J., Li, C., Mihalcea, L.C. (eds) Schubert Calculus and Its Applications in Combinatorics and Representation Theory. ICTSC 2017. Springer Proceedings in Mathematics & Statistics, vol 332. Springer, Singapore. https://doi.org/10.1007/978-981-15-7451-1_9
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