Pure parts of the mixed Hodge structures of character varieties of indivisible type

Abstract

We fix integers $k> 0$ and $n>0$. For a $k$-punctured Riemann surface $\Sigma \setminus \{ p_1,\ldots,p_k \}$ and a $k$-tuple $\boldsymbol{\mu}=(\mu^1,\ldots,\mu^k)$ of partitions of $n$, we can define the character variety of type $\boldsymbol{\mu}$. In this paper, we consider the case where $\Sigma=\mathbb{P}^1$ and $\boldsymbol{\mu}$ is indivisible (i.e. $\mathrm{g.c.d.}(\boldsymbol{\mu})=1$). For the case, we prove the purity conjecture due to Hausel, that is, the pure parts of the mixed Hodge structures of the character variety is isomorphic to the ordinary rational cohomology groups of the quiver variety of type $\boldsymbol{\mu}$.