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arXiv · 0803.0237

Monodromy Groups of Hurwitz-type Problems

Daniel Allcock·Chris Hall
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Abstract

We solve the Hurwitz monodromy problem for degree-4 covers. That is, the Hurwitz space H_{4,g} of all simply branched covers of P^1 of degree 4 and genus g is an unramified cover of the space P_{2g+6} of (2g+6)-tuples of distinct points in P^1. We determine the monodromy of pi_1(P_{2g+6}) on the points of the fiber. This turns out to be the same problem as the action of pi_1(P_{2g+6}) on a certain local system of Z/2-vector spaces. We generalize our result by treating the analogous local system with Z/N coefficients, gcd(3,N)=1, in place of Z/2. This in turn allows us to answer a question of Ellenberg concerning families of Galois covers of P^1 with deck group (Z/N)^2:S_3.

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Daniel Allcock, Chris Hall. 2008-03-03. Monodromy Groups of Hurwitz-type Problems. https://arxiv.org/abs/0803.0237

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