SMRI Algebra and Geometry Online: Kim -- Optimal regularity of mapping class group actions on the circle

SMRI Algebra and Geometry Online

’Optimal regularity of mapping class group actions on the circle’
Sang-hyun Kim (Korea Institute for Advanced Study)

Wednesday Mar 2, 2022 01:00 PM AEDT
Online via Zoom
Register:
https://uni-sydney.zoom.us/meeting/register/tZEkcu6hrTsiH9DzT5Z6_R6RMfLeSIVnYC9v

Abstract: We prove that for each finite index subgroup H of the mapping class group of a 
closed hyperbolic surface, and for each real number r>1 there does not exist a faithful 
C^r-action (in Hoelder’s sense) of H on a circle. For this, we partially determine the 
optimal regularity of faithful actions by right-angled Artin groups on a circle. (Joint 
with Thomas Koberda and Cristobal Rivas).

Biography: Sang-hyun Kim works at Korea Institute for Advanced Study as Professor in the 
School of Mathematics since 2019. Before this, he worked at Seoul National University, 
KAIST, Tufts University, the University of Texas at Austin and MSRI. He received Ph.D in 
2007 at Yale University under the supervision of Andrew Casson. His research interests 
focus on the interplay between geometric group theory and low--dimensional topology, 
particularly motivated by right-angled Artin groups and manifold diffeomorphism groups. 
He was selected as the Scientist of the Month by the Korean Ministry of Science and ICT 
in 2020.

Note
These seminars will be recorded, including participant questions (participants only when 
asking questions), and uploaded to the SMRI YouTube Channel 
https://www.youtube.com/c/SydneyMathematicalResearchInstituteSMRI

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