Paper 2, Section II, I

Riemann Surfaces
Part II, 2012

Let XX be the algebraic curve in C2\mathbb{C}^{2} defined by the polynomial p(z,w)=zd+wd+1p(z, w)=z^{d}+w^{d}+1 where dd is a natural number. Using the implicit function theorem, or otherwise, show that there is a natural complex structure on XX. Let f:XCf: X \rightarrow \mathbb{C} be the function defined by f(a,b)=bf(a, b)=b. Show that ff is holomorphic. Find the ramification points and the corresponding branching orders of ff.

Assume that ff extends to a holomorphic map g:YC{}g: Y \rightarrow \mathbb{C} \cup\{\infty\} from a compact Riemann surface YY to the Riemann sphere so that g1()=Y\Xg^{-1}(\infty)=Y \backslash X and that gg has no ramification points in g1()g^{-1}(\infty). State the Riemann-Hurwitz formula and apply it to gg to calculate the Euler characteristic and the genus of YY.