The Lefschetz condition conjecture for Braden–MacPherson sheaves

Let wW^w\in{\widehat{\mathcal W}} and suppose that charK>N(w)\operatorname{char} K>N(w). For every xwx\le w, let

ix ⁣:B(w)xB(w)xi_x\colon\overline{\mathcal B}(w)_x\to\overline{\mathcal B}(w)^x

be the indicated map between the costalk and stalk of the reduced Braden–MacPherson sheaf. Recall that a map f ⁣:ABf\colon A\to B of graded free K[t]K[t]-modules satisfies the Lefschetz condition with center lZl\in\mathbb Z if multiplication by tnt^n induces an isomorphism

(cokerf){ln}(cokerf){l+n}(\operatorname{coker}f)_{\{l-n\}}\stackrel{\sim}{\to}(\operatorname{coker}f)_{\{l+n\}}

for every n1n\ge1. The Lefschetz condition conjecture. For all xwx\le w, the map ixi_x satisfies the Lefschetz condition with center l(w)l(w). This conjecture proposes a Hard Lefschetz-type symmetry for the stalk–costalk maps of Braden–MacPherson sheaves in characteristic greater than N(w)N(w). The supplied text does not state whether it has been resolved.

Sources & referencesView supporting material

Primary source

Peter Fiebig, “An upper bound on the exceptional characteristics for Lusztig's character formula”, arXiv:0811.1674 (2009).

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