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UID:20251123T182923EST-7958N0a45u@132.216.98.100
DTSTAMP:20251123T232923Z
DESCRIPTION:Title: Entropy\, metrics and quasi-morphisms.\n\nAbstract:\n\nO
 ne of the mainstream and modern tools in the study of non-abelian groups a
 re quasi-morphisms. These are functions from a group to the reals which sa
 tisfy homomorphism condition up to a bounded error. Nowadays they are used
  in many fields of mathematics. For instance\, they are related to bounded
  cohomology\, stable commutator length\, metrics on diffeomorphism groups\
 , displacement of sets in symplectic topology\, dynamics\, knot theory\, o
 rderability\, and the study of mapping class groups and of concordance gro
 up of knots.\n\nLet S be a compact oriented surface. In this talk\, I will
  discuss several invariant metrics and quasi-morphisms on the identity com
 ponent Diff0(S\,area) of the group of area-preserving diffeomorphisms of S
 . In particular\, I will show that some quasi-morphisms on Diff0(S\,area) 
 are related to the topological entropy. More precisely\, I will discuss a 
 construction of infinitely many linearly independent quasi-morphisms on Di
 ff0(S\,area) whose absolute values bound from below the topological entrop
 y. If time permits\, I will define a bi-invariant metric on this group\, c
 alled the entropy metric\, and show that it is unbounded. Based on a joint
  work with M. Marcinkowski.\n\n \n
DTSTART:20190918T190000Z
DTEND:20190918T200000Z
LOCATION:Room 1104\, Burnside Hall\, CA\, QC\, Montreal\, H3A 0B9\, 805 rue
  Sherbrooke Ouest
SUMMARY:Michael Brandenbursky (Ben-Gurion University) 
URL:/mathstat/channels/event/michael-brandenbursky-ben
 -gurion-university-300715
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