Rational pullbacks of Galois covers

Research output: Contribution to journalResearch articleContributedpeer-review

Contributors

  • Pierre Dèbes - , Université de Lille (Author)
  • Joachim König - , Korea National University of Education (Author)
  • François Legrand - , Institute of Algebra (Author)
  • Danny Neftin - , Technion-Israel Institute of Technology (Author)

Abstract

The finite subgroups of PGL 2(C) are shown to be the only finite groups G with this property: for some integer r (depending on G), all Galois covers X→PC1 of group G can be obtained by pulling back those with at most r branch points along non-constant rational maps PC1→PC1. For G⊂ PGL 2(C) , it is in fact enough to pull back one well-chosen cover with at most 3 branch points. A consequence of the converse for inverse Galois theory is that, for G⊄ PGL 2(C) , letting the branch point number grow provides truly new Galois realizations F/ C(T) of G. Another application is that the “Beckmann–Black” property that “any two Galois covers of PC1 with the same group G are always pullbacks of another Galois cover of group G” only holds if G⊂ PGL 2(C).

Details

Original languageEnglish
Pages (from-to)1507-1531
Number of pages25
JournalMathematische Zeitschrift
Volume299
Issue number3-4
Publication statusPublished - Dec 2021
Peer-reviewedYes

Keywords

ASJC Scopus subject areas

Keywords

  • Galois covers, Inverse Galois theory, Rational pullback