Reductive covers of klt varieties

• Lukas Braun ^[1] ; Joaquín Moraga ^[2]
  1. [1] University of Innsbruck

     University of Innsbruck

     Innsbruck, Austria

     
  2. [2] University of California System

     University of California System

     Estados Unidos

     
• Localización: Revista matemática iberoamericana, ISSN 0213-2230, Vol. 40, Nº 5, 2024, págs. 1701-1730
• Idioma: inglés
• DOI: 10.4171/RMI/1494
• Enlaces
  • Texto completo
• Resumen

  • In this article, we study G-covers of klt varieties, where G is a reductive group. First, we exhibit an example of a klt singularity admitting a PGL n (K)-cover that is not of klt type. Then, we restrict ourselves to G-quasi-torsors, a special class of G-covers that behave like G-torsors outside closed subsets of codimension two. Given a G-quasi-torsor X→Y, where G is a finite extension of a torus T, we show that X is of klt type if and only if Y is of klt type. We prove a structural theorem for T-quasi-torsors over normal varieties in terms of Cox rings. As an application, we show that every sequence of T-quasi-torsors over a variety with klt type singularities is eventually a sequence of T-torsors. This is the torus version of a result due to Greb–Kebekus–Peternell regarding finite quasi-torsors of varieties with klt type singularities. On the contrary, we show that in any dimension there exists a sequence of finite quasi-torsors and T-quasi-torsors over a klt type variety, such that infinitely many of them are not torsors. We show that every variety with klt type singularities is a quotient of a variety with canonical factorial singularities. We prove that a variety with Zariski locally toric singularities is indeed the quotient of a smooth variety by a solvable group. Finally, motivated by the work of Stibitz, we study the optimal class of singularities for which the previous results hold.