Perverse filtration on Hilbert schemes via upward flow

Abstract

We explicitly compute the perverse Leray filtration on the top cohomology of the Hilbert scheme of points on $\Sigma \times \mathbb{C}$, for any connected smooth projective curve $\Sigma$. The computation is carried out in the natural basis given by the ${\mathbb{C}}^{\ast }$-upward-flow cycles. The result is described by a simple symmetric-function dictionary: upward-flow classes correspond to products of complete homogeneous symmetric functions, while the perverse-homogeneous basis corresponds to products of power-sum symmetric functions. This gives an explicit triangular change-of-basis between the two bases.

arXiv comment21 pages, minor changes in the introduction