E-Polynomials of Generic $\text{GL}_n\rtimes\!<\!\sigma\!>\!~$-Character Varieties: Branched Case

Abstract

For any branched double covering of compact Riemann surfaces, we consider the associated character varieties that are unitary in the global sense, which we call $\text{GL}_n\rtimes\!<\!\sigma\!>\!~$-character varieties. We restrict the monodromies around the ramification points to generic semi-simple conjugacy classes contained in $\text{GL}_n\sigma$, and compute the E-polynomials of these character varieties using the character table of $\text{GL}_n(q)\rtimes\!<\!\sigma\!>\!$. The result is expressed as the inner product of certain symmetric functions associated to the wreath products $(\mathbb{Z}/2\mathbb{Z})^N\rtimes\mathfrak{S}_N$. We are then led to a conjectural formula for the mixed Hodge polynomial, which involves (modified) Macdonald polynomials and wreath Macdonald polynomials.