58:57
published on March 21, 2025
Analytic delta invariant and weighted Kähler geometry Lecture 1
By Thibaut Delcroix
Shear coordinates of Weil-Petersson circle homeomorphisms
By Yilin Wang
Appears in collections : Jean Morlet Chair - Conference - Renormalization and Visualization in Geometry, Dynamics and number theory / Chaire Jean-Morlet - Conférence - Renormalisation et visualisation en géométrie, dynamique et théorie des nombres, ECM 2024 Invited Speakers
The shear coordinate is a countable coordinate system to describe increasing self-maps of the unit circle, which is furthermore invariant under modular transformations. Characterizations of circle homeomorphism and quasisymmetric homeomorphisms were obtained by D. Šarić. We are interested in characterizing Weil-Petersson circle homeomorphisms using shears. This class of homeomorphisms arises from the Kähler geometry on the universal Teichmüller space. For this, we introduce diamond shear which is the minimal combination of shears producing WP homeomorphisms. Diamond shears are closely related to the log-Lambda length introduced by R. Penner, which can be viewed as a renormalized length of an infinite geodesic. We obtain sharp results comparing the class of circle homeomorphisms with square summable diamond shears with the Weil-Petersson class and Hölder classes. We also express the Weil-Petersson metric tensor and symplectic form in terms of infinitesimal shears and diamond shears. This talk is based on joint work with Dragomir Šarić and Catherine Wolfram. See https://arxiv.org/abs/2211.11497.
