# Rudvalis group

In the area of modern algebra known as group theory, the Rudvalis group Ru is a sporadic simple group of order

214 · 33 · 53 ·· 13 · 29
= 145926144000
≈ 1×1011.

## History

Ru is one of the 26 sporadic groups and was found by Arunas Rudvalis (1973, 1984) and constructed by John H. Conway and David B. Wales (1973). Its Schur multiplier has order 2, and its outer automorphism group is trivial.

In 1982 Robert Griess showed that Ru cannot be a subquotient of the monster group. Thus it is one of the 6 sporadic groups called the pariahs.

## Properties

The Rudvalis group acts as a rank 3 permutation group on 4060 points, with one point stabilizer being the Ree group 2F4(2), the automorphism group of the Tits group. This representation implies a strongly regular graph srg(4060, 2304, 1328, 1208). That is, each vertex has 2304 neighbors and 1755 non-neighbors, any two adjacent vertices have 1328 common neighbors, while any two non-adjacent ones have 1208 (Griess 1998, p. 125).

Its double cover acts on a 28-dimensional lattice over the Gaussian integers. The lattice has 4×4060 minimal vectors; if minimal vectors are identified whenever one is 1, i, –1, or –i times another, then the 4060 equivalence classes can be identified with the points of the rank 3 permutation representation. Reducing this lattice modulo the principal ideal

[math](1 + i)\ [/math]

gives an action of the Rudvalis group on a 28-dimensional vector space over the field [math]\mathbb F_2[/math] with 2 elements. Duncan (2006) used the 28-dimensional lattice to construct a vertex operator algebra acted on by the double cover.

(Parrott 1976) characterized the Rudvalis group by the centralizer of a central involution. (Aschbacher Smith) gave another characterization as part of their identification of the Rudvalis group as one of the quasithin groups.

## Maximal subgroups

(Wilson 1984) found the 15 conjugacy classes of maximal subgroups of Ru as follows:

• 2F4(2) = 2F4(2)'.2
• 26.U3(3).2
• (22 × Sz(8)):3
• 23+8:L3(2)
• U3(5):2
• 21+4+6.S5
• PSL2(25).22
• A8
• PSL2(29)
• 52:4.S5
• 3.A6.22
• 51+2:
• L2(13):2
• A6.22
• 5:4 × A5