E-polynomials of character varieties for real curves

We calculate the E-polynomial for a class of the (complex) character varieties ${\mathcal{M}}_n^{\tau }$ associated to a genus $g$ Riemann surface $\mathrm{\Sigma }$ equipped with an orientation reversing involution $\tau$. Our formula expresses the generating function $\sum_{n=1}^{\infty} E($\mathcal{M}$_n^{\tau}) T^n$ as the plethystic logarithm of a product of sums indexed by Young diagrams. The proof uses point counting over finite fields, emulating Hausel and Rodriguez-Villegas.