Andersen Filtration and Hard Lefschetz

On the space of homomorphisms from a Verma module to an indecomposable tilting module of the BGG-category O we define a natural filtration following Andersen and establish a formula expressing the dimensions of the filtration steps in terms of coefficients of Kazhdan-Lusztig polynomials.Comment: English version of math.RT/0604589, v3 revised translatio

Quantitative measurement of the surface charge density

We present a method of measuring the charge density on dielectric surfaces. Similar to electrostatic force microscopy we record the electrostatic interaction between the probe and the sample surface, but at large tip-sample distances. For calibration we use a pyroelectric sample which allows us to alter the surface charge density by a known amount via a controlled temperature change. For proof of principle we determined the surface charge density under ambient conditions of ferroelectric lithium niobate

Parabolic category O, perverse sheaves on Grassmannians, Springer fibres and Khovanov homology

For a fixed parabolic subalgebra p of gl(n,C) we prove that the centre of the principal block O(p) of the parabolic category O is naturally isomorphic to the cohomology ring of the corresponding Springer fibre. We give a diagrammatic description of O(p) for maximal parabolic p and give an explicit isomorphism to Braden's description of the category Perv_B(G(n,n)) of perverse sheaves on Grassmannians. As a consequence Khovanov's algebra H^n is realised as the endomorphism ring of some object from Perv_B(G(n,n)) which corresponds under localisation and the Riemann-Hilbert correspondence to a full projective-injective module in the corresponding category $O(p)$. From there one can deduce that Khovanov's tangle invariants are obtained from the more general functorial invariants involving category O by restriction.Comment: 39 pages, 9 figures, added a few remark

Khovanov-Rozansky homology via a canopolis formalism

In this paper, we describe a canopolis (i.e. categorified planar algebra) formalism for Khovanov and Rozansky's link homology theory. We show how this allows us to organize simplifications in the matrix factorizations appearing in their theory. In particular, it will put the equivalence of the original definition of Khovanov-Rozansky homology and the definition using Soergel bimodules in a more general context, allow us to give a new proof of the invariance of triply graded homology and give new analysis of the behavior of triply graded homology under the Reidemeister IIb move.Comment: 24 pages, 7 figures. v3: edited introduction and fixed diagram 1, plus minor change

Quantitative analysis of ferroelectric domain imaging with piezoresponse force microscopy

The contrast mechanism for ferroelectric domain imaging via piezoresponse force microscopy (PFM) is investigated. A novel analysis of PFM measurements is presented which takes into account the background caused by the experimental setup. This allows, for the first time, a quantitative, frequency independent analysis of the domain contrast which is in good agreement with the expected values for the piezoelectric deformation of the sample and satisfies the generally required features of PFM imaging

Modular Koszul duality

We prove an analogue of Koszul duality for category $\mathcal{O}$ of a reductive group $G$ in positive characteristic $\ell$ larger than 1 plus the number of roots of $G$. However there are no Koszul rings, and we do not prove an analogue of the Kazhdan--Lusztig conjectures in this context. The main technical result is the formality of the dg-algebra of extensions of parity sheaves on the flag variety if the characteristic of the coefficients is at least the number of roots of $G$ plus 2.Comment: 62 pages; image displays best in pd