Paper 3, Section II, G

Riemann Surfaces
Part II, 2011

State the Classical Monodromy Theorem for analytic continuations in subdomains of the plane.

Let n,rn, r be positive integers with r>1r>1 and set h(z)=zn1h(z)=z^{n}-1. By removing nn semi-infinite rays from C\mathbb{C}, find a subdomain UCU \subset \mathbb{C} on which an analytic function h1/rh^{1 / r} may be defined, justifying this assertion. Describe briefly a gluing procedure which will produce the Riemann surface RR for the complete analytic function h1/rh^{1 / r}.

Let ZZ denote the set of nnth roots of unity and assume that the natural analytic covering map π:RC\Z\pi: R \rightarrow \mathbb{C} \backslash Z extends to an analytic map of Riemann surfaces π~:R~C\tilde{\pi}: \tilde{R} \rightarrow \mathbb{C}_{\infty}, where R~\tilde{R} is a compactification of RR and C\mathbb{C}_{\infty} denotes the extended complex plane. Show that π~\tilde{\pi} has precisely nn branch points if and only if rr divides nn.