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Nigel P. Byott and Lindsay N. Childs
Fixed-point free pairs of homomorphisms and nonabelian Hopf-Galois structures view print
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Published: |
October 6, 2012 |
Keywords: |
Hopf-Galois structure; abelian extensions; semidirect product |
Subject: |
12F10 (primary), 16W30 (secondary) |
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Abstract
Given finite groups Γ and G of order n, regular embeddings
from Γ to the holomorph of G yield Hopf-Galois structures on a
Galois extension L|K of fields with Galois group Γ. Here we
consider regular embeddings that arise from fixed-point free pairs of
homomorphisms from Γ to G. If G is a complete group, then all
regular embeddings arise from fixed-point free pairs. For all Γ,
G of order n = p(p-1) with p a safeprime, we compute the number
of Hopf-Galois structures that arise from fixed-point free pairs, and
compare the results with a count of all Hopf-Galois structures
obtained by T. Kohl. Using the idea of fixed-point free pairs, we
characterize the abelian Galois groups Γ of even order or order a
power of p, an odd prime, for which L|K admits a nonabelian Hopf
Galois structure. The paper concludes with some new classes of
abelian groups Γ for which every Hopf-Galois structure has type
Γ (and hence is abelian).
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Author information
Nigel P. Byott:
College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK
N.P.Byott@ex.ac.uk
Lindsay N. Childs:
Department of Mathematics and Statistics, University at Albany, Albany, NY 12222
lchilds@albany.edu
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