Abstract
We show that a conformal connection on a closed oriented surface \(\Sigma \) of negative Euler characteristic preserves precisely one conformal structure and is furthermore uniquely determined by its unparametrised geodesics. As a corollary it follows that the unparametrised geodesics of a Riemannian metric on \(\Sigma \) determine the metric up to constant rescaling. It is also shown that every conformal connection on the \(2\)-sphere lies in a complex \(5\)-manifold of conformal connections, all of which share the same unparametrised geodesics.
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Notes
As usual, by an affine torsion-free connection on \(\Sigma \) we mean a torsion-free connection on \(T\Sigma \).
We define \(\varepsilon _{ij}=-\varepsilon _{ji}\) with \(\varepsilon _{12}=1\).
In order to keep notation uncluttered we omit writing \(\lambda ^*\) for pull-backs by \(\lambda \).
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Acknowledgments
This paper would not have come into existence without several very helpful discussions with Nigel Hitchin. I would like to warmly thank him here. I also wish to thank Vladimir Matveev for references and the anonymous referee for her/his careful reading and useful suggestions.
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Research for this article was carried out while the author was visiting the Mathematical Institute at the University of Oxford as a postdoctoral fellow of the Swiss NSF, PA00P2_142053. The author would like to thank the Mathematical Institute for its hospitality.
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Mettler, T. Geodesic rigidity of conformal connections on surfaces. Math. Z. 281, 379–393 (2015). https://doi.org/10.1007/s00209-015-1489-5
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DOI: https://doi.org/10.1007/s00209-015-1489-5