English

A module isomorphism between $H^*_T(G/P)\otimes H^*_T(P/B)$ and $H^*_T(G/B)$

Algebraic Topology 2015-09-03 v2

Abstract

We give an explicit (new) morphism of modules between HT(G/P)HT(P/B)H^*_T(G/P) \otimes H^*_T(P/B) and HT(G/B)H^*_T(G/B) and prove (the known result) that the two modules are isomorphic. Our map identifies submodules of the cohomology of the flag variety that are isomorphic to each of HT(G/P)H^*_T(G/P) and HT(P/B)H^*_T(P/B). With this identification, the map is simply the product within the ring HT(G/B)H^*_T(G/B). We use this map in two ways. First we describe module bases for HT(G/B)H^*_T(G/B) that are different from traditional Schubert classes and from each other. Second we analyze a WW-representation on HT(G/B)H^*_T(G/B) via restriction to subgroups WPW_P. In particular we show that the character of the Springer representation on HT(G/B)H^*_T(G/B) is a multiple of the restricted representation of WPW_P on HT(P/B)H^*_T(P/B).

Keywords

Cite

@article{arxiv.1409.0834,
  title  = {A module isomorphism between $H^*_T(G/P)\otimes H^*_T(P/B)$ and $H^*_T(G/B)$},
  author = {Elizabeth Drellich and Julianna Tymoczko},
  journal= {arXiv preprint arXiv:1409.0834},
  year   = {2015}
}