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Published online by Cambridge University Press:  18 November 2019

Gaël Cousin
GMA-IME, Universidade Federal Fluminense, Campus do Gragoatá, Niterói, RJ, Brazil (
Viktoria Heu
IRMA, 7 rue René Descartes, 67084Strasbourg, France (


The germ of the universal isomonodromic deformation of a logarithmic connection on a stable $n$-pointed genus $g$ curve always exists in the analytic category. The first part of this article investigates under which conditions it is the analytic germification of an algebraic isomonodromic deformation. Up to some minor technical conditions, this turns out to be the case if and only if the monodromy of the connection has finite orbit under the action of the mapping class group. The second part of this work studies the dynamics of this action in the particular case of reducible rank 2 representations and genus $g>0$, allowing to classify all finite orbits. Both of these results extend recent ones concerning the genus 0 case.

Research Article
© Cambridge University Press 2019

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The authors would like to warmly thank Gwenaël Massuyeau for discussions around the mapping class group. We are also grateful to the anonymous referee for useful suggestions. This work took place at IRMA and LAREMA. It was supported by ANR-13-BS01-0001-01, ANR-13-JS01-0002-01 and Labex IRMIA.


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