Séminaire à venir - Juin 2025
Le séminaire aura lieu un mercredi du mois (exceptionnellement deux exposés) de 14h à 15h et 15h30 à 16h30 à l'Institut Henri Poincaré à Paris. Pour télécharger l'affiche du mois: juin.pdf.
- 18/06/2025 - Richard Schwartz (Brown University)
salle Olga Ladyjenskaïa (ex-salle 01)
Titre: The
optimal paper Moebius band
Resumé: If
the number \(L\) is large you can
take a \(1 \times L\) rectangular strip, smoothly twist it in space,
and
glue the ends together so as to make an embedded paper Moebius band. If
\(L\) is too small this is impossible. In this talk I will explain why
\(L > \sqrt{3}\) is a necessary and sufficient condition for the
existence of a smoothly embedded paper Moebius band. This is the
solution to the 1977 conjecture of B. Halpern and C. Weaver. I will
also explain why a sequence of \(L\)-minimizing examples must converge
to
an equilateral triangle.
- 18/06/2025 - Simion Filip (University of Chicago)
salle Olga Ladyjenskaïa (ex-salle 01)
Titre: Measure
and Topological Rigidity Beyond Homogeneous Dynamics
Resumé:
To study the asymptotic behavior of orbits of a dynamical system, one
can look at orbit closures or invariant measures. When the underlying
system has a homogeneous structure, usually coming from a Lie group,
with appropriate assumptions a wide range of rigidity theorems show
that ergodic invariant measures and orbit closures have to be
well-behaved and can often be classified. I will describe joint work
with Brown, Eskin, and Rodriguez-Hertz, which establishes rigidity
results for quite general smooth dynamical systems having some
hyperbolicity. I will also explain some of the necessary assumptions as
well as the homogeneous structures that emerge.