Mini-Workshop: Superexpanders and Their Coarse Geometry

  • Ana Khukhro

    Université de Neuchâtel, Switzerland
  • Tim de Laat

    Universität Münster, Germany
  • Mikael de la Salle

    École Normale Supérieure de Lyon, France
Mini-Workshop: Superexpanders and Their Coarse Geometry cover

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It is a deep open problem whether all expanders are superexpanders. In fact, it was already a major challenge to prove the mere existence of superexpanders. However, by now, some classes of examples are known: Lafforgue’s expanders constructed as sequences of finite quotients of groups with strong Banach property (T), the examples coming from zigzag products due to Mendel and Naor, and the recent examples coming from group actions on compact manifolds. The methods which are used to construct superexpanders are typically functional analytic in nature, but also rely on arguments from geometry and combinatorics. Another important aspect of the study of superexpanders is their (coarse) geometry, in particular in order to distinguish them from each other.

The aim of this workshop was to bring together researchers working on superexpanders and their coarse geometry from different perspectives, with the aim of sharing expertise and stimulating new research.

Cite this article

Ana Khukhro, Tim de Laat, Mikael de la Salle, Mini-Workshop: Superexpanders and Their Coarse Geometry. Oberwolfach Rep. 15 (2018), no. 2, pp. 1117–1160

DOI 10.4171/OWR/2018/19