Paper 1, Section II, H

Riemann Surfaces
Part II, 2014

If XX is a Riemann surface and p:YXp: Y \rightarrow X is a covering map of topological spaces, show that there is a conformal structure on YY such that p:YXp: Y \rightarrow X is analytic.

Let f(z)f(z) be the complex polynomial z51z^{5}-1. Consider the subspace RR of C2=C×C\mathbb{C}^{2}=\mathbb{C} \times \mathbb{C} given by the equation w2=f(z)w^{2}=f(z), where (z,w)(z, w) denotes coordinates in C2\mathbb{C}^{2}, and let π:RC\pi: R \rightarrow \mathbb{C} be the restriction of the projection map onto the first factor. Show that RR has the structure of a Riemann surface which makes π\pi an analytic map. If τ\tau denotes projection onto the second factor, show that τ\tau is also analytic. [You may assume that RR is connected.]

Find the ramification points and the branch points of both π\pi and τ\tau. Compute also the ramification indices at the ramification points.

Assuming that it is possible to add a point PP to RR so that X=R{P}X=R \cup\{P\} is a compact Riemann surface and τ\tau extends to a holomorphic map τ:XC\tau: X \rightarrow \mathbb{C}_{\infty} such that τ1()={P}\tau^{-1}(\infty)=\{P\}, compute the genus of X.X .