文摘
For each natural number?\(d\), the space \(R_d\) of rational maps of degree?\(d\) on the Riemann sphere has the structure of a complex manifold. The topology of these manifolds has been extensively studied. The recent development of Oka theory raises some new and interesting questions about their complex structure. We apply geometric invariant theory to the cases of degree?2 and?3, studying a double action of the M?bius group on \(R_d\). The action on \(R_2\) is transitive, implying that \(R_2\) is an Oka manifold. The action on \(R_3\) has \({\mathbb C}\) as a categorical quotient; we give an explicit formula for the quotient map and describe its structure in some detail. We also show that \(R_3\) enjoys the holomorphic flexibility properties of strong dominability and \({\mathbb C}\)-connectedness.