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Nick Gill

Publications and source records attributed to Nick Gill.

50 records · Page 3Linked to original sources
arXiv2012

Orientable regular maps with Euler characteristic divisible by few primes

Let $G$ be a $(2,m,n)$-group and let $x$ be the number of distinct primes dividing $χ$, the Euler characteristic of $G$. We prove, first, that, apart from a finite number of known exceptions, a non-abelian simple composition factor $T$ of $G$ is a finite group of Lie type with rank $n\leq x$. This result is proved using new results connecting the prime graph of $T$ to the integer $x$. We then study the particular cases $x=1$ and $x=2$. We give a general structure statement for $(2,m,n)$-groups which have Euler characteristic a prime power, and we construct an infinite family of these objects. We also give a complete classification of those $(2,m,n)$-groups which are almost simple and for which the Euler characteristic is a prime power (there are four such). Finally we study those $(2,m,n)$-groups which are almost simple and for which the Euler characteristic is a product of two prime powers. All such groups which are not isomorphic to $PSL_2(q)$ or $PGL_2(q)$ are completely classified.

math.GR↗
arXiv2012

Bounds on the diameter of Cayley graphs of the symmetric group

In this paper we are concerned with the conjecture that, for any set of generators S of the symmetric group of degree n, the word length in terms of S of every permutation is bounded above by a polynomial of n. We prove this conjecture for sets of generators containing a permutation fixing at least 37% of the points.

math.GR↗
arXiv2010

Growth of small generating sets in SL_n(Z/pZ)

Let G=SL_n. Let K=Z/pZ, p a prime. Let A\subset G(K) generate G(K). Suppose that |A| 0. Then |A A A|>>|A|^{1+ε}, where epsilon>0 and the implied constant depend only on n and delta.

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arXiv2009

Real and strongly real classes in finite linear groups

We classify the real and strongly real conjugacy classes in $GL_n(q)$, $SL_n(q)$, $PGL_n(q)$, $PSL_n(q)$, and all quasi-simple covers of $PSL_n(q)$. In each case we give a formula for the number of real, and the number of strongly real, conjugacy classes.

math.GR↗
arXiv2008

Transitive projective planes and 2-rank

Suppose that a group $G$ acts transitively on the points of a non-Desarguesian plane, $\mathcal{P}$. We prove first that the Sylow 2-subgroups of $G$ are cyclic or generalized quaternion. We also prove that $\mathcal{P}$ must admit an odd order automorphism group which acts transitively on the set of points of $\mathcal{P}$.

math.GR↗
arXiv2008

Reversible maps and composites of involutions in groups of piecewise linear homeomorphisms of the real line

An element of a group is \emph{reversible} if it is conjugate to its own inverse, and it is \emph{strongly reversible} if it is conjugate to its inverse by an involution. A group element is strongly reversible if and only if it can be expressed as a composite of two involutions. In this paper the reversible maps, the strongly reversible maps, and those maps that can be expressed as a composite of involutions are determined in certain groups of piecewise linear homeomorphisms of the real line.

math.GR↗
arXiv2007

Transitive projective planes

A long-standing conjecture is that any transitive finite projective plane is Desarguesian. We make a contribution towards a proof of this conjecture by showing that a group acting transitively on the the points of a non-Desarguesianprojective plane must not contain any components.

math.GR↗
arXiv2007

Large dimensional classical groups and linear spaces

Suppose that a group $G$ has socle $L$ a simple large-rank classical group. Suppose furthermore that $G$ acts transitively on the set of lines of a linear space $\mathcal{S}$. We prove that, provided $L$ has dimension at least 25, then $G$ acts transitively on the set of flags of $\mathcal{S}$ and hence the action is known. For particular families of classical groups our results hold for dimension smaller than 25. The group theoretic methods used to prove the result (described in Section 3) are robust and general and are likely to have wider application in the study of almost simple groups acting on finite linear spaces.

math.GR↗
arXiv2006

Nilpotent Singer Groups

Let $N$ be a nilpotent group normal in a group $G$. Suppose that $G$ acts transitively upon the points of a finite non-Desarguesian projective plane $\mathcal{P}$. We prove that, if $\mathcal{P}$ has square order, then $N$ must act semi-regularly on $\mathcal{P}$. In addition we prove that if a finite non-Desarguesian projective plane $\mathcal{P}$ admits more than one nilpotent group which is regular on the points of $\mathcal{P}$ then $\mathcal{P}$ has non-square order and the automorphism group of $\mathcal{P}$ has odd order.

math.GR↗
arXiv2006

Linear spaces with significant characteristic prime

Let $G$ be a group with socle a simple group of Lie type defined over the finite field with $q$ elements where $q$ is a power of the prime $p$. Suppose that $G$ acts transitively upon the lines of a linear space $\mathcal{S}$. We show that if $p$ is {\it significant} then $G$ acts flag-transitively on $\mathcal{S}$ and all examples are known.

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arXiv2006

Polar spaces and embeddings of classical groups

Given polar spaces $(V,β)$ and $(V,Q)$ where $V$ is a vector space over a field $K$, $β$ a reflexive sesquilinear form and $Q$ a quadratic form, we have associated classical isometry groups. Given a subfield $F$ of $K$ and an $F$-linear function $L:K\to F$ we can define new spaces $(V,Lβ)$ and $(V,LQ)$ which are polar spaces over $F$. The construction so described gives an embedding of the isometry groups of $(V,β)$ and $(V,Q)$ into the isometry groups of $(V,Lβ)$ and $(V,LQ)$. In the finite field case under certain added restrictions these subgroups are maximal and form the so called {\it field extension subgroups} of Aschbacher's class $\curlyc{3}$ \cite{aschbacher}. We give precise descriptions of the polar spaces so defined and their associated isometry group embeddings. In the finite field case our results give extra detail to the account of maximal field extension subgroups given by Kleidman and Liebeck \cite[p112]{kl}.

math.GR↗