# 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 Conway and Wales (1973). Its Schur multiplier has order 2, and its outer automorphism group is trivial.

Ru is one of the 6 sporadic simple groups called the pariahs because (Griess 1982) showed that it is not a subquotient of the monster group.

## Properties

The Rudvalis group acts as a rank 3 permutation group on 4060 points, with one point stabilizer the Ree group 2F4(2), the automorphism group of the Tits group. This representation implies a strongly regular graph in which each vertex has 2304 neighbors and 1755 non-neighbors. Two adjacent vertices have 1328 common neighbors; 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 if 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

$(1 + i)\$

gives an action of the Rudvalis group on a 28-dimensional vector space over the field 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 (2004) 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:[25]
• L2(13):2
• A6.22
• 5:4 × A5