Symmetry, Integrability and Geometry: Methods and Applications (SIGMA)


SIGMA 16 (2020), 125, 42 pages      arXiv:1910.13535      https://doi.org/10.3842/SIGMA.2020.125

A Map Between Moduli Spaces of Connections

Frank Loray a and Valente Ramírez b
a) Univ Rennes, CNRS, IRMAR - UMR 6625, F-35000 Rennes, France
b) University of Twente, Department of Applied Mathematics, 7500 AE Enschede, The Netherlands

Received December 17, 2019, in final form November 24, 2020; Published online December 02, 2020

Abstract
We are interested in studying moduli spaces of rank 2 logarithmic connections on elliptic curves having two poles. To do so, we investigate certain logarithmic rank 2 connections defined on the Riemann sphere and a transformation rule to lift such connections to an elliptic curve. The transformation is as follows: given an elliptic curve $C$ with elliptic quotient $\pi\colon C\to{\mathbb P}^1$, and the logarithmic connection $(E,\nabla)$ on ${\mathbb P}^1$, we may pullback the connection to the elliptic curve to obtain a new connection $(\pi^*E, \pi^*\nabla)$ on $C$. After suitable birational modifications we bring the connection to a particular normal form. The whole transformation is equivariant with respect to bundle automorphisms and therefore defines a map between the corresponding moduli spaces of connections. The aim of this paper is to describe the moduli spaces involved and compute explicit expressions for the above map in the case where the target space is the moduli space of rank 2 logarithmic connections on an elliptic curve $C$ with two simple poles and trivial determinant.

Key words: moduli spaces; parabolic connection; logarithmic connection; parabolic vector bundle; parabolic Higgs bundle; elliptic curve.

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