The induction formula for fundamental classes in equivariant Lagrangian homology

Let XX and XX' be the varieties in the induction diagram, with a map g\relationshipsWXg\relationships W\to X' and the induced map

ξ ⁣:UTX,(w,l)(g(w),l),\xi\colon U\to \operatorname{T}^*X',\qquad (w,l')\mapsto (g(w),l'),

where

U={(w,l)W×XTXldg(w)=0}.U=\{(w,l')\in W\times_{X'}\operatorname{T}^*X'\mid l'\circ \mathrm{d}g(w)=0\}.

Let [X]LagrGm(TX)[X]\in \operatorname{Lagr}^{\mathbb{G}_{\mathrm{m}}}(\operatorname{T}^*X) be the fundamental class of XX. For every ΛLagrGm(TX)\Lambda\in\operatorname{Lagr}^{\mathbb{G}_{\mathrm{m}}}(\operatorname{T}^*X'), choose a general point xΛ=(x,l)Λx_{\Lambda}=(x',l')\in\Lambda such that ξ1(x,l)\xi^{-1}(x',l') is smooth. Induction formula.

Ind([X])=ΛLagrGm(TX)(1)dim(ΛX)χ(ξ1(xΛ))[Λ].\operatorname{Ind}([X])=\sum_{\Lambda'\in\operatorname{Lagr}^{\mathbb{G}_{\mathrm{m}}}(\operatorname{T}^*X')}(-1)^{\dim(\Lambda'\cap X')}\chi\bigl(\xi^{-1}(x_{\Lambda'})\bigr)[\Lambda'].

This formula would describe the induction map on the fundamental class in terms of Euler characteristics of the fibers of ξ\xi, and is intended to clarify the connection between constructible functions on the seminilpotent stack and the top cohomological Hall algebra. The source does not state whether the conjecture is resolved.

Sources & referencesView supporting material

Primary source

Lucien Hennecart, “Geometric realisations of the unipotent enveloping algebra of a quiver”, arXiv:2209.06552 (2024).

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