Yves Stalder

  1. Fixed point properties in the space of marked groups.

    Authors: Yves Stalder
    Subjects: Group Theory
    Abstract

    We explain, following Gromov, how to produce uniform isometric actions of
    groups starting from isometric actions without fixed point, using common
    ultralimits techniques. This gives in particular a simple proof of a result by
    Shalom: Kazhdan's property (T) defines an open subset in the space of marked
    finitely generated groups.

  2. Limits of Baumslag-Solitar groups and dimension estimates in the space of marked groups.

    Authors: Luc Guyot, Yves Stalder
    Subjects: Group Theory
    Abstract

    We prove that the limits of Baumslag-Solitar groups which we previously
    studied are non-linear hopfian C*-simple groups with infinitely many twisted
    conjugacy classes. We exhibit infinite presentations for these groups, classify
    them up to group isomorphism, describe their automorphisms and discuss the word
    and conjugacy problems. Finally, we prove that the set of these groups has
    non-zero Hausforff dimension in the space of marked groups on two generators.

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