70 research outputs found
A reducible characteristic variety in type A
We show that simple highest weight modules for sl_12 may have reducible
characteristic variety. This answers a question of Borho-Brylinski and Joseph
from 1984. The relevant singularity under Beilinson-Bernstein localization is
the (in)famous Kashiwara-Saito singularity. We sketch the rather indirect route
via the p-canonical basis, W-graphs and decomposition numbers for perverse
sheaves that led us to examine this singularity.Comment: 13 pages, comments welcom
On an analogue of the James conjecture
We give a counterexample to the most optimistic analogue (due to Kleshchev
and Ram) of the James conjecture for Khovanov-Lauda-Rouquier algebras
associated to simply-laced Dynkin diagrams. The first counterexample occurs in
type A_5 for p = 2 and involves the same singularity used by Kashiwara and
Saito to show the reducibility of the characteristic variety of an intersection
cohomology D-module on a quiver variety. Using recent results of Polo one can
give counterexamples in type A in all characteristics.Comment: 12 pages. v2: final versio
Local Hodge theory of Soergel bimodules
We prove the local hard Lefschetz theorem and local Hodge-Riemann bilinear
relations for Soergel bimodules. Using results of Soergel and K\"ubel one may
deduce an algebraic proof of the Jantzen conjectures. We observe that the
Jantzen filtration may depend on the choice of non-dominant regular deformation
direction.Comment: 54 pages, v3: further minor changes. Final version to appear in Acta.
Mat
The anti-spherical category
We study a diagrammatic categorification (the "anti-spherical category") of
the anti-spherical module for any Coxeter group. We deduce that Deodhar's
(sign) parabolic Kazhdan-Lusztig polynomials have non-negative coefficients,
and that a monotonicity conjecture of Brenti's holds. The main technical
observation is a localisation procedure for the anti-spherical category, from
which we construct a "light leaves" basis of morphisms. Our techniques may be
used to calculate many new elements of the -canonical basis in the
anti-spherical module.Comment: Best viewed in colo
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