Robert Silhol | Searcharxiv

arXiv2019

Energy distribution of harmonic 1-forms and Jacobians of Riemann surfaces with a short closed geodesic

We study the energy distribution of harmonic 1-forms on a compact hyperbolic Riemann surface $S$ where a short closed geodesic is pinched. If the geodesic separates the surface into two parts, then the Jacobian torus of $S$ develops into a torus that splits. If the geodesic is nonseparating then the Jacobian torus of $S$ degenerates. The aim of this work is to get insight into this process and give estimates in terms of geometric data of both the initial surface $S$ and the final surface, such as its injectivity radius and the lengths of geodesics that form a homology basis. As an invariant we introduce new families of symplectic matrices that compensate for the lack of full dimensional Gram-period matrices in the noncompact case.

math.DG↗

arXiv2014

Quasiconformal embeddings of Y-pieces

In this paper we construct quasiconformal embeddings from Y-pieces that contain a short boundary geodesic into degenerate ones. These results are used in a companion paper to study the Jacobian tori of Riemann surfaces that contain small simple closed geodesics.

math.DG↗

arXiv2007

Multi-geodesic tessellations, fractional Dehn twists and uniformization of algebraic curves

Identifying parallel sides of a collection of Euclidean polygons yields a flat surface with cone points of angles multiples of 2 pi, naturally a compact Riemann surface but also an algebraic curve, and a hyperbolic surface. In general two different metrics on a surface have no geodesic arcs in common, but in special cases the surface is decomposed into polygons geodesic for both the flat and the hyperbolic metric. This is the case for certain surfaces which are translation and half-turn tiled by an Euclidean rectangle. We explore them in this paper. Their multi-geodesic tessellation provides a mechanical way to reconstruct a Fuchsian group for them; allows to describe their Teichmueller disk in terms of Fenchel-Nielsen coordinates; allows for an interpretation in terms of fractional Dehn twists of the natural PSL_2(Z) action on the PSL_2(R)-orbit of such surfaces. In many cases the tiling by rectangles allows to recover an equation for the corresponding algebraic curve, providing a bridge between the algebraic equation and the hyperbolic structure deduced from the multi-geodesic tessellation; in other words solving the uniformization problem for such curves. In fact it also gives a scheme to do uniformization for infinitely many families of curves. We also discuss some number theoretic aspects.

math.GT↗