A Geometric Model for Hochschild Homology of Soergel Bimodules

An important step in the calculation of the triply graded link theory of Khovanov and Rozansky is the determination of the Hochschild homology of Soergel bimodules for SL(n). We present a geometric model for this Hochschild homology for any simple group G, as equivariant intersection homology of B × Borbit closures in G. We show that, in type A these orbit closures are equivariantly formal for the conjugation T -action. We use this fact to show that in the case where the corresponding orbit closure is smooth, this Hochschild homology is an exterior algebra over a polynomial ring on generators whose degree is explicitly determined by the geometry of the orbit closure, and describe its Hilbert series, proving a conjecture of Jacob Rasmussen.