Necessary condition for the existence of a simple closed geodesic on a regular tetrahedron in the spherical space

In the spherical space the curvature of the tetrahedron’s faces equals 1, and the curvature of the whole tetrahedron is concentrated into its vertices and faces. The intrinsic geometry of this tetrahedron depends on the value α of faces angle, where π/3 < α ⩽ 2π/3. The simple (without points of self-intersection) closed geodesic has the type (p,q) on a tetrahedron, if this geodesic has p points on each of two opposite edges of the tetrahedron, q points on each of another two opposite edges, and (p+q) points on each edges of the third pair of opposite one. For any coprime integers (p,q), we present the number αp, q (π/3 < αp, q < 2π/3) such that, on a regular tetrahedron in the spherical space with the faces angle of value α > αp, q, there is no simple closed geodesic of type (p,q)

Earthquakes and Graftings of Hyperbolic Surface laminations

We study compact hyperbolic surface laminations. These are a generalisation of closed hyperbolic surfaces, which appear to be more suited to the study of Teichmüller theory than arbitrary non-compact surfaces. We show that the Teichmüller space of any non-trivial hyperbolic surface lamination is infinite dimensional. In order to prove this result, we study the theory of deformations of hyperbolic surfaces, and we derive a new formula for the derivative of the length of a simple closed geodesic with respect to the action of grafting. This formula complements those derived by McMullen [ 24], in terms of the Weil–Petersson metric, and by Wolpert [ 34], for the case of earthquakes.

Symmetry of topographs of Markoff forms

The Markoff spectrum is defined as the set of normalized values of arithmetic minima of indefinite quadratic forms. In the theory of the Markoff spectrum we observe various kinds of symmetry. Each of Conway’s topographs of quadratic forms which give values in the discrete part of the Markoff spectrum has a special infinite path consisting of edges. It has symmetry with respect to a translation along the path and countable central symmetries by which the path is invariant. We prove that these properties are obtained from the fact that the path is a discretization of a geodesic in the upper half-plane which corresponds to a value of the discrete part of the Markoff spectrum and projects to a simple closed geodesic on the once punctured torus with the highest degree of symmetry.

ON THE EXISTENCE OF CLOSED GEODESICS ON TWO-SPHERES

In [7] J. Franks proves the existence of infinitely many closed geodesics for every Riemannian metric on S2 which satisfies the following condition: there exists a simple closed geodesic for which Birkhoff's annulus map is defined. In particular, all metrics with positive Gaussian curvature have this property. Here we prove the existence of infinitely many closed geodesics for every Riemannian metric on S2 which has a simple closed geodesic for which Birkhoff's annulus map is not defined. Combining this with J. Franks's result and with the fact that every Riemannian metric on S2 has a simple closed geodesic one obtains the existence of infinitely many closed geodesics for every Riemannian metric on S2.

Non-smooth geodesic flows and the earthquake flow on Teichmüller space

Thurston generalized the notion of a twist deformation about a simple closed geodesic on a hyperbolic Riemann surface to a twisting or shearing along a much more complicated object called a measure geodesic lamination. This new deformation is called an earthquake and it generates a flow on the tangent bundle of Teichmüller space.In this paper we study the earthquake flow. We show that the flow is not smooth and that it is not the geodesic flow for an affine connection. We also derive the explicit form of the system of differential equations which earthquake trajectories satisfy.