Nilpotent Orbits of Orthogonal Groups over p-adic Fields, and the DeBacker Parametrization


For local non-archimedean fields k of sufficiently large residual characteristic, we explicitly parametrize and count the rational nilpotent adjoint orbits in each algebraic orbit of orthogonal and special orthogonal groups. We separately give an explicit algorithmic construction for representatives of each orbit. We then, in the general setting of groups GLn(D), SLn(D) (where D is a central division algebra over k) or classical groups, give a new characterisation of the “building set” (defined by DeBacker) of an \(\mathfrak {sl}_{2}(k)\)-triple in terms of the building of its centralizer. Using this, we prove our construction realizes DeBacker’s parametrization of rational nilpotent orbits via elements of the Bruhat-Tits building.

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Correspondence to Monica Nevins.

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Monica Nevins’s research is supported by a Discovery Grant from NSERC Canada.

Presented by: Michela Varagnolo

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Bernstein, T., Ma, JJ., Nevins, M. et al. Nilpotent Orbits of Orthogonal Groups over p-adic Fields, and the DeBacker Parametrization. Algebr Represent Theor 23, 2033–2058 (2020).

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  • p-adic groups
  • Nilpotent orbits
  • DeBacker classification
  • Quadratic forms
  • Bruhat-Tits buildings

Mathematics Subject Classification (2010)

  • 20G25 (17B08, 17B45)