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Thomas Barthelmé
Norbert Wiener Assistant Professor
Thomas Barthelmé
Contact Info:
Tufts University
Department of Mathematics
503 Boston Avenue
Bromfield-Pearson
Room 109
Medford, MA 02155

Email @tufts.edu:
thomas.barthelme
Phone: 617-627-2678

Expertise:
Finsler geometry, Anosov flows, Negatively-curved spaces, Laplace-like operators

Research:
I am working in geometry and dynamical systems, and, mostly, I'm interested in the interaction between the two. For instance, what can be deduced about the geometry of a space, knowing its dynamics? And vice-versa. Among the objects we like to study in relation with this question are the geodesic flow and objects constructed from it (like the entropy, or some invariant measures like the Bowen-Margulis measure) of course, but also global analytical tools like the Laplacian.

I study these type of questions in Finsler geometry, which is a generalization of Riemannian geometry where the metric is given by a family of norms not necessarily coming from a scalar product. As Finsler geometry is much wider than Riemannian geometry, the links between geometry and dynamics are generally either less strong, or even harder to prove. But this wider generality leads to my two favorite phenomena:

  • Some surprising rigidity results
  • Some new behaviors that initially didn't seem to be possible (did you know that there exists Finsler metrics on the sphere with only two periodic geodesics?)
Finsler geometry also lacks some of the global analysis tools that Riemannian geometry enjoys. As part of my Ph.D., I introduced a Laplace operator in Finsler geometry. This definition is very nice (I think) and simple enough to allow the study of this operator.

There is a lot of things that can be studied about a Laplacian. Among the things I started studying are the construction of harmonic measures on (Finsler) negatively curved manifolds and what happens when the harmonic measures coincide with the Bowen-Margulis measure (for Riemannian metric, it implies that the space is locally symmetric). I am also interested in more specifically Laplacian questions, like finding bounds on the eigenvalues.

Outside of geometry, I also study Anosov flows (i.e., flows that locally looks like the geodesic flow of a negatively curved manifold) for themselves. With questions related to either their regularity (and what can be deduced from regularity assumptions) or topological questions for Anosov flows in 3-manifolds.