University of London, Birkbeck College
Department:Economics, Mathematics and Statistics
Position:Department Member
Ben started following the journal Journal of Group Theory.
Ben started following the work of Jessica Leech, University of Cambridge, Philosophy.
Ben started following the work of 3 people.
Papers
Generation of finite simple groups with an application to groups acting on Beauville surfaces
with Kay Magaard and Christopher Parker
We develop theorems which produce a multitude of hyperbolic triples for the finite classical groups. We apply these theorems to prove that every quasisimple group except Alt(5) and SL_2(5) is a Beauville group. In particular, we settle a conjecture of Bauer, Catanese and Grunewald which asserts that all non-abelian finite simple groups except for the alternating group Alt(5) are Beauville groups.
Some exceptional Beauville structures
submitted to the Mathematische Zeitschrift. Also available on the arxiv.
We first show that every quasisimple sporadic group possesses an unmixed strongly real Beauville structure aside from the Mathieu groups M11 and M23 (and possibly 2B and M). To do this we give the first generic construction of objects of this kind which in princicpal may be adapted to a number of other cases. We go on to show that no almost simple sporadic group possesses a mixed Beauville structure. We then go on to use the exceptional nature of the alternating group A6 to give a strongly real Beauville structure for this group correcting an earlier error of Fuertes
and Gonzalez-Diez. In doing so we complete the classication of alternating groups that possess strongly real Beauville structures. We conclude by discussing mixed Beauville structures of the
groups A6 : 2 and A6:2^2.
New Upper Bounds on the Spreads of the Sporadic Simple Groups
To appear in Communications in Algebra. Note that, compared to the version to be published, this version gives better bounds for M23 and the Baby Monster and contains an additional section giving some concluding remarks.
Let G be a group. We say that G has spread r if for any set of distinct nontrivial elements {x1, . . . , xr} ⊂ G there exists an element y ∈ G with the property that <xi, y> = G for every 1 ≤ i ≤ r. Few bounds on the spread of finite simple groups are known. In this paper we present improved upper bounds for the spread of many of the larger sporadic simple groups, in some cases improving on the best known upper bound by several orders of magnitude.
Some Design Theoretic Results on the Conway Group ·0
Electronic Journal of Combinatorics 17(1) 2010
Let \Omega be a set of 24 points with the structure of the (5,8,24) Steiner system, S, defined on it. The automorphism group of S acts on famous Leech lattice, as does the binary Golay code defined by S. Let A,B \subset\Omega be subsets of size four (“tetrads”). The structure of S forces each tetrad to define a certain partition of into six tetrads called a sextet. For each tetrad Conway defined a certain automorphism of Leech lattice that extend the group generated by the above to the
automorphism group of the lattice. For the tetrad A he denoted this automorphism \zeta_A. It is well known that for \zeta_A and \zeta_B to commute is sufficient to have A and B belong to the same sextet. We extend this to a necessary and sufficient condition, namely \zeta_A and \zeta_B will commute if and only if A\cup B is contained in a block of S. We go on extend this result to similar conditions for other elements of the group and show how neatly these results restrict to certain subgroups.
Symmetric Representation of the Elements of the Conway Group ·0
Joint with my PhD supervisor, RT Curtis. This is a preprint version of the published article: Journal of Symbolic Computation, 44 (2009) p.1044-1067.
In this paper we represent each element of the Conway group ·0 as a permutation on 24 letters from the Mathieu group M24, followed by a sign change on a codeword of the binary Golay code (multiplication by a diagonal matrix taking the value -1 on the positions of a codeword and 1 otherwise), followed by a word of length at most four in a highly symmetric generating set.We describe an algorithm for multiplying elements represented in this way, that we have implemented in Magma. We include a detailed description of Λ4, the sets of 24 mutually orthogonal 4-vectors in the Leech lattice Λ often referred to as frames of reference or crosses, as they are instrumental to our procedure. In particular we describe the 19 orbits of M24 on these crosses.
A Note On Monomial Representations Linear Groups
a slightly old version of a paper recently accepted by `Communications in Algebra'
A matrix is said to be monomial if every row and column has only one non-zero entry. Let G be a group. A representation \rho: G \rightarrow GL_n(C) is said to be a monomial representation of G if there exists a basis with respect to which \rho(g) is a monomial matrixfor every g\in G. We use elementary methods to classify the irreducible monomial representations of the groups L_2(q), L_3(q) and their natural decorations.
Recent Progress in the Symmetric Generation of Groups
A survey article accepted for the proceedings of the conference `Groups St Andrews 2009'
Many groups posses highly symmetric generating sets that are naturally endowed with an underlying combinatorial structure. Such generating sets can prove to be extremely useful both theoretically in providing new existence proofs for groups and practically by providing succinct means of representing group elements. We give a survey of results obtained in the study of these symmetric generating sets. In keeping with earlier surveys on this matter, we emphasize the sporadic simple groups.
Symmetric Generation of Coxeter Groups
Joint with J\"{u}rgen M\"{u}ller, Archiv der Mathematik 93 (2009) 1-10
We provide involutory symmetric generating sets of finitely generated Coxeter groups, fulfilling a suitable finiteness condition, which in particular is fulfilled in the finite, affine and compact hyperbolic cases.
Symmetric Presentations of Coxeter Groups
A slightly old version of a paper submitted to the "Proceedings of the Edinburgh Mathematical Society"
We apply the techniques of symmetric generation to establish the
standard presentations of the finite simply laced irreducible finite
Coxeter groups, that is the Coxeter groups of types An, Dn and
En and show that these are naturally arrived at purely through
consideration of certain natural actions of symmetric groups. We
go on to use these techniques to provide explicit representations of these groups.
Extensions of Symmetric Generating Sets
in preparation
In this paper we review existing methods of extending symmetric generating sets, namely Transitive Extensions and Subset Extensions before introducing a new approach using wreath products. We proceed to give examples of this new construction, most notably for the unitary groups U_3(2^r).
