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Ruling out (160, 54, 18) difference sets in some nonabelian groups
Author(s) -
Alexander J.,
Balasubramanian R.,
Martin J.,
Monahan K.,
Pollatsek H.,
Sen A.
Publication year - 2000
Publication title -
journal of combinatorial designs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.618
H-Index - 34
eISSN - 1520-6610
pISSN - 1063-8539
DOI - 10.1002/1520-6610(2000)8:4<221::aid-jcd1>3.0.co;2-6
Subject(s) - sylow theorems , mathematics , abelian group , order (exchange) , coset , quotient , combinatorics , image (mathematics) , finite group , normal subgroup , group (periodic table) , pure mathematics , discrete mathematics , chemistry , organic chemistry , finance , artificial intelligence , computer science , economics
We prove the following theorems. Theorem A. Let G be a group of order 160 satisfying one of the following conditions. (1) G has an image isomorphic to D 20 × Z 2 (for example, if G ≃ D 20 × K). (2) G has a normal 5‐Sylow subgroup and an elementary abelian 2‐Sylow subgroup. (3) G has an abelian image of exponent 2, 4, 5, or 10 and order greater than 20. Then G cannot contain a (160, 54, 18) difference set. Theorem B. Suppose G is a nonabelian group with 2‐Sylow subgroup S and 5‐Sylow subgroup T and contains a (160, 54, 18) difference set. Then we have one of three possibilities. (1) T is normal, |ϕ( S )| = 8, and one of the following is true: (a) G = S × T and S is nonabelian; (b) G has a D 10 image; or (c) G has a Frobenius image of order 20. (2) G has a Frobenius image of order 80. (3) G is of index 6 in A Γ L (1, 16). To prove the first case of Theorem A, we find the possible distribution of a putative difference set with the stipulated parameters among the cosets of a normal subgroup using irreducible representations of the quotient; we show that no such distribution is possible. The other two cases are due to others. In the second (due to Pott) irreducible representations of the elementary abelian quotient of order 32 give a contradiction. In the third (due to an anonymous referee), the contradiction derives from a theorem of Lander together with Dillon's “dihedral trick.” Theorem B summarizes the open nonabelian cases based on this work. © 2000 John Wiley & Sons, Inc. J Combin Designs 8: 221–231, 2000