The Hard Lefschetz decomposition conjecture for Bruhat-graph sheaves

From papers

Choose a generic line in VV^\ast and let ρ:SR[T]\rho:S\to{\mathbb R}[T] be the corresponding graded surjection, with TT of degree 22. For an SS-module MM, set MT=MSR[T]M_T=M\otimes_S{\mathbb R}[T]. Let B(x)Tδy{\mathscr B}(x)^{\delta y}_T be the indicated quotient module associated with the stalk and costalk of B(x){\mathscr B}(x) at yy. The Hard Lefschetz decomposition conjecture. For every x,yWx,y\in{\mathcal W} with y<xy<x, the R[T]{\mathbb R}[T]-module B(x)Tδy{\mathscr B}(x)^{\delta y}_T is isomorphic to a direct sum of modules of the form

(R[T]/Tn+1){(l(x)l(y))+n},n0.\left({\mathbb R}[T]/T^{n+1}\right)\{-(l(x)-l(y))+n\},\qquad n\geq 0.

This is the algebraic Hard Lefschetz-type statement used to imply the genericity conjecture, and hence the degree conjecture. The supplied text gives no resolution status.

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Sources & referencesView supporting material

Primary source

Peter Fiebig, “Kazhdan-Lusztig combinatorics via sheaves on Bruhat graphs”, arXiv:math/0512311 (2006).

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