Moduli spaces of vector bundles with fixed determinant over a real curve

Abstract: Let $(\Sigma,\tau)$ denote a Riemann surface of genus $g \geq 2$ equipped with an anti-holomorphic involution $\tau$. In this paper we study the topology of the moduli space $M(r,\xi)^\tau$ of stable Real vector bundles over $(\Sigma,\tau)$ of rank $r$ and fixed determinant $\xi$ of degree coprime to $r$. We prove that $M(r,\xi)^{\tau}$ is an orientable and monotone Lagrangian submanifold of the complex moduli space $M(r,\xi)$ so it determines an object in the appropriate Fukaya category. We derive recursive formulas for the mod $2$ Betti numbers of $M(r,\xi)^\tau$ and compute mod $p$ Betti numbers for odd $p$ through a range of degrees. We deduce that if $r$ is even and $ g >>0$, then $M(r,\xi)^{\tau}$ and $M(r,\xi')^{\tau}$ have non-isomorphic cohomology groups unless $\xi$ and $\xi'$ have equivalent Stieffel-Whitney classes modulo automorphisms of $(\Sigma,\tau)$. If $r$ is even, and $g>>0$ is even, we prove that the Betti numbers of $M(r,\xi)^{\tau}$ distinguish topological types of $(\Sigma, \tau; \xi)$. If $r=2$ and $g$ is odd, we compute all mod $p$ Betti numbers of $M(2,\xi)^\tau$. MR 32L05, 14P25.