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ON INVOLUTIONS AND INDICATORS OF FINITE ORTHOGONAL GROUPS

Part of: Combinatorics Linear algebraic groups and related topics Representation theory of groups

Published online by Cambridge University Press:  30 May 2018

GREGORY K. TAYLOR  and
C. RYAN VINROOT
GREGORY K. TAYLOR
Affiliation:
Department of Mathematics, Statistics, and Computer Science (MC249), University of Illinois at Chicago, 851 South Morgan Street, Chicago, IL 60680-7045, USA email [email protected]
C. RYAN VINROOT*
Affiliation:
Department of Mathematics, College of William and Mary, P. O. Box 8795, Williamsburg, VA 23187-8795, USA email [email protected]
*
✉[email protected]
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Abstract

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We study the numbers of involutions and their relation to Frobenius–Schur indicators in the groups $\text{SO}^{\pm }(n,q)$ and $\unicode[STIX]{x1D6FA}^{\pm }(n,q)$. Our point of view for this study comes from two motivations. The first is the conjecture that a finite simple group $G$ is strongly real (all elements are conjugate to their inverses by an involution) if and only if it is totally orthogonal (all Frobenius–Schur indicators are 1), and we observe this holds for all finite simple groups $G$ other than the groups $\unicode[STIX]{x1D6FA}^{\pm }(4m,q)$ with $q$ even. We prove computationally that for small $m$ this statement indeed holds for these groups by equating their character degree sums with the number of involutions. We also prove a result on a certain twisted indicator for the groups $\text{SO}^{\pm }(4m+2,q)$ with $q$ odd. Our second motivation is to continue the work of Fulman, Guralnick, and Stanton on generating functions and asymptotics for involutions in classical groups. We extend their work by finding generating functions for the numbers of involutions in $\text{SO}^{\pm }(n,q)$ and $\unicode[STIX]{x1D6FA}^{\pm }(n,q)$ for all $q$, and we use these to compute the asymptotic behavior for the number of involutions in these groups when $q$ is fixed and $n$ grows.

Keywords

orthogonal groups over finite fieldsFrobenius–Schur indicatorsinvolutionsgenerating functionsasymptotic enumeration

MSC classification

Primary: 20G40: Linear algebraic groups over finite fields
Secondary: 20C33: Representations of finite groups of Lie type 05A15: Exact enumeration problems, generating functions 05A16: Asymptotic enumeration
Type
Research Article
Information
Journal of the Australian Mathematical Society , Volume 105 , Issue 3 , December 2018 , pp. 380 - 416
Copyright
© 2018 Australian Mathematical Publishing Association Inc. 

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