# Members & Former Members

## Project

26Projective surfaces, Segre structures and the Hitchin component for PSL(n,R)
68Minimal Lagrangian connections and related structures

We establish a one-to-one correspondence between Finsler structures on the $$2$$-sphere with constant curvature $$1$$ and all geodesics closed on the one hand, and Weyl connections on certain spindle orbifolds whose symmetric Ricci curvature is positive definite and all of whose geodesics closed on the other hand. As an application of our duality result, we show that suitable holomorphic deformations of the Veronese embedding $$\mathbb{CP}(a_1,a_2)\to \mathbb{CP}(a_1,(a_1+a_2)/2,a_2)$$ of weighted projective spaces provide examples of Finsler $$2$$-spheres of constant curvature and all geodesics closed.

 Journal Journal of the Institute of Mathematics of Jussieu Publisher Cambridge University Press Volume to appear Link to preprint version Link to published version

Related project(s):
68Minimal Lagrangian connections and related structures

We associate a flow $$\phi$$ to a solution of the vortex equations on a closed oriented Riemannian 2-manifold $$(M,g)$$ of negative Euler characteristic and investigate its properties. We show that $$\phi$$ always admits a dominated splitting and identify special cases in which $$\phi$$ is Anosov. In particular, starting from holomorphic differentials of fractional degree, we produce novel examples of Anosov flows on suitable roots of the unit tangent bundle of $$(M,g)$$.

 Journal Ergodic Theory and Dynamical Systems Publisher Cambridge University Press Volume 42 Pages 1781--1806 Link to preprint version Link to published version

Related project(s):
68Minimal Lagrangian connections and related structures

We show that the metrisability of an oriented projective surface is equivalent to the existence of pseudo-holomorphic curves. A projective structure $\mathfrak{p}$ and a volume form $\sigma$ on an oriented surface $M$ equip the total space of a certain disk bundle $Z \to M$ with a pair $(J_{\mathfrak{p}},\mathfrak{J}_{\mathfrak{p},\sigma})$ of almost complex structures. A conformal structure on $M$ corresponds to a section of $Z\to M$ and $\mathfrak{p}$ is metrisable by the metric $g$ if and only if $[g] : M \to Z$ is a pseudo-holomorphic curve with respect to $J_{\mathfrak{p}}$ and $\mathfrak{J}_{\mathfrak{p},dA_g}$.

 Journal Mathematische Zeitschrift Publisher Springer Link to preprint version Link to published version

We show that a properly convex projective structure $$\mathfrak{p}$$ on a closed oriented surface of negative Euler characteristic arises from a Weyl connection if and only if $$\mathfrak{p}$$ is hyperbolic. We phrase the problem as a non-linear PDE for a Beltrami differential by using that $$\mathfrak{p}$$ admits a compatible Weyl connection if and only if a certain holomorphic curve exists. Turning this non-linear PDE into a transport equation, we obtain our result by applying methods from geometric inverse problems. In particular, we use an extension of a remarkable $$L^2$$-energy identity known as Pestov's identity to prove a vanishing theorem for the relevant transport equation.

 Journal Analysis & PDE Publisher Mathematical Sciences Publishers Volume 13 Pages 1073--1097 Link to preprint version Link to published version

We introduce a new family of thermostat flows on the unit tangent bundle of an oriented Riemannian 2-manifold. Suitably reparametrised, these flows include the geodesic flow of metrics of negative Gauss curvature and the geodesic flow induced by the Hilbert metric on the quotient surface of divisible convex sets. We show that the family of flows can be parametrised in terms of certain weighted holomorphic differentials and investigate their properties. In particular, we prove that they admit a dominated splitting and we identify special cases in which the flows are Anosov. In the latter case, we study when they admit an invariant measure in the Lebesgue class and the regularity of the weak foliations.

 Journal Mathematische Annalen Publisher Springer Volume 373 Pages 553--580 Link to preprint version Link to published version
• 1