On the Teichm\"uller geodesic generated by the L-shaped translation surface tiled by three squares

TL;DR

This paper investigates a specific family of genus 2 Riemann surfaces generated by the Teichmüller geodesic flow on an L-shaped surface tiled by three squares, providing conditions to identify their period matrices.

Contribution

It characterizes the period matrices of these surfaces and solves the Schottky problem for the family, revealing automorphism constraints and explicit conditions.

Findings

Only the original 3-square-tiled surface admits a non-hyperelliptic automorphism.

Explicit necessary and sufficient conditions for period matrices are provided.

The classical method for computing period matrices cannot be applied to most surfaces in the family.

Abstract

We study the one parameter family of genus 2 Riemann surfaces defined by the orbit of the L-shaped translation surface tiled by three squares under the Teichm\"uller geodesic flow. These surfaces are real algebraic curves with three real components. We are interested in describing these surfaces by their period matrices. We show that the only Riemann surface in that family admitting a non-hyperelliptic automorphism comes from the 3-square-tiled translation surface itself. This makes the computation of an exact expression for period matrices of other Riemann surfaces in that family by the classical method impossible. We nevertheless give the solution to the Schottky problem for that family: we exhibit explicit necessary and sufficient conditions for a Riemann matrix to be a period matrix of a Riemann surface in the family, involving the vanishing of a genus 3 theta characteristic on a family of double covers.