• Cocharacter-closure and spherical buildings 

      [OWP-2015-12] Bate, Michael; Herpel, Sebastian; Martin, Benjamin; Röhrle, Gerhard (Mathematisches Forschungsinstitut Oberwolfach, 2015-07-29)
      Let k be a field, let G be a reductive k-group and V an affine k-variety on which G acts. In this note we continue our study of the notion of cocharacter-closed G(k)-orbits in V. In earlier work we used a ...
    • Cocharacter-Closure and the Rational Hilbert-Mumford Theorem 

      [OWP-2014-16] Bate, Michael; Herpel, Sebastian; Martin, Benjamin; Röhrle, Gerhard (Mathematisches Forschungsinstitut Oberwolfach, 2014-12-20)
      For a field k, let G be a reductive k-group and V an affine k-variety on which G acts. Using the notion of cocharacter-closed G(k)-orbits in V , we prove a rational version of the celebrated Hilbert-Mumford ...
    • Edifices: Building-like Spaces Associated to Linear Algebraic Groups; In memory of Jacques Tits 

      [OWP-2023-04] Bate, Michael; Martin, Benjamin; Röhrle, Gerhard (Mathematisches Forschungsinstitut Oberwolfach, 2023-06-19)
      Given a semisimple linear algebraic k-group G, one has a spherical building ΔG, and one can interpret the geometric realisation ΔG(R) of ΔG in terms of cocharacters of G. The aim of this paper is to ...
    • G-complete reducibility in non-connected groups 

      [OWP-2013-09] Bate, Michael; Herpel, Sebastian; Martin, Benjamin; Röhrle, Gerhard (Mathematisches Forschungsinstitut Oberwolfach, 2013-04-10)
      In this paper we present an algorithm for determining whether a subgroup H of a non-connected reductive group G is G-completely reducible. The algorithm consists of a series of reductions; at each step, we perform ...
    • On Overgroups of Distinguished Unipotent Elements in Reductive Groups and Finite Groups of Lie Type 

      [OWP-2024-05] Bate, Michael; Böhm, Sören; Martin, Benjamin; Röhrle, Gerhard (Mathematisches Forschungsinstitut Oberwolfach, 2024-06-18)
      Suppose G is a simple algebraic group defined over an algebraically closed field of good characteristic p. In 2018 Korhonen showed that if H is a connected reductive subgroup of G which contains a distinguished unipotent ...
    • On Unipotent Radicals of Pseudo-Reductive Groups 

      [OWP-2017-12] Bate, Michael; Martin, Benjamin; Röhrle, Gerhard; Stewart, David I. (Mathematisches Forschungsinstitut Oberwolfach, 2017-04-27)
      We establish some results on the structure of the geometric unipotent radicals of pseudo-reductive k-groups. In particular, let k be a purely inseparable field extension of k of degree pe and let G denote the ...
    • The Subgroup Structure of Pseudo-Reductive Groups 

      [OWP-2024-08] Bate, Michael; Martin, Benjamin; Röhrle, Gerhard; Sercombe, Damian (Mathematisches Forschungsinstitut Oberwolfach, 2024-07-31)
      Let k be a field. We investigate the relationship between subgroups of a pseudo-reductive k-group G and its maximal reductive quotient G, with applications to the subgroup structure of G. Let k/k be the minimal ...