Elementary groups and stability for Jordan pairs

A stability condition for Jordan algebras and, more generally, for Jordan pairs is introduced which extends the first stable range condition for associative and alternative rings. It is formulated in terms of the projective elementary group of a Jordan pair and has most of the properties expected from the associative case. The proofs involve a new kind of fourfold quasi-inverse.     

Steinberg modules and Donkin pairs

First we prove that in characteristicp>0 a module with good filtration for a group of type E₆ restricts to a module with good filtration for a group of type F₄. Thus we confirm a conjecture of Brundan for one more case. Our method relies on the canonical Frobenius splittings of Mathieu. Next we settle the remaining cases, with a computer-aided variation on the old method of Donkin.     

The Steinberg formula for orbit groups

The aim of this note is to give a direct proof of the fact that the Steinberg formula holds for the Vaserstein symbol and the universal weak Mennicke symbol. We also give an alternate proof of the fact that the Steinberg formula holds for the Vaserstein symbol.     

Jordan forms for mutually annihilating nilpotent pairs

In this paper we completely characterize all possible pairs of Jordan canonical forms for mutually annihilating nilpotent pairs, i.e. pairs (A,B) of nilpotent matrices such that AB=BA=0.     

Finiteness conditions in Jordan pairs

To Nathan Jacobson on his 80^th birthday     

Extreme pairs for finite groups

Let G be a finite group with.O₂(G) = 1. If V is a faithful GF(2)G-module, then 𝔓 (G,V) is the set of elementary abelian 2-subgroups A of G with m(A) ? m(V/C_V(A)). A pair G,V is an extreme pair if G = < 𝔓 (G,V)>. Such pairs often appears in analysis of 2-local subgroups of characteristic 2-type groups. The following theorem is the main result of this paper.     

On the Steinberg module of Chevalley groups

For a simple Chevalley group G an explicit version of the Solomon-Tits theorem is proved by describing the generators of the kernel of the map Z[G(K)]S_K, where K is any field and where S_K is the Steinberg module of the group G(K). As a corollary it is shown that if is a Euclidean domain whose fraction field is K, then S_K is cyclic as a G() module when G is either a classical group or an exceptional group of type E₆, or E₇.Acknowledgement I would like to thank Matt Emerton, Özlem Imamoglu, Paul Gunnells for several helpful comments.     

Isomorphisms of Steinberg groups over commutative rings

LetA andR be commutative rings, andm andn be integers3. It is proved that, if :St _m (A)St _n (R) is an isomorphism, thenm=n. Whenn4, we have: (1) Every isomorphism :St _n(A)St _n(R) induces an isomorphism:E _n (A)E _n (R), and is uniquely determined by; (2) IfSt _n (A) St _n (R) thenK _2.n (A)K _2.n (R); (3) Every isomorphismE _n (A) E _n (R) can be lifted to an isomorphismSt _n(A)St _n(R); (4)St _n(A) St _n(R) if and only ifAR. For the casen=3, ifSt ₃(A) andSt ₃(R) are respectively central extensions ofE ₃(A) andE ₃ (R), then the above (1) and (2) hold.The Project supported by National Natural Science Foundation of China     

Modular representations of simple Jordan pairs

Omsk. Translated fromSibirskii Matematicheskii Zhurnal, Vol. 32, No. 2, pp. 200–203, March–April, 1991.     

The Steinberg variety and representations of reductive groups

We give an overview of some of the main results in geometric representation theory that have been proved by means of the Steinberg variety. Steinberg's insight was to use such a variety of triples in order to prove a conjectured formula by Grothendieck. The Steinberg variety was later used to give an alternative approach to Springer's representations and played a central role in the proof of the Deligne–Langlands conjecture for Hecke algebras by Kazhdan and Lusztig.     

Finite presentability of Steinberg groups over group rings

LetA be a finitely generated commutative -algebra with Krull dimensiond, and let be an arbitrary finite group. It is proved that the Steinberg groupSt _n (A) is finitely presented whenevern4. If, in addition,nd+3, andK ₁ (A) andK ₂ (A) are finitely generated, thenE _n (A) andGL _n (A) are finitely presented.The Project supported by National Natural Science Foundation of China.     

Equations arising from Jordan *-derivation pairs

Summary. We study certain functional equations derived from the definition of a Jordan *-derivation pair. More precisely, if A is a complex *-algebra and M is a bimodule over A, having the structure of a complex vector space compatible with the structure of A, such that implies m = 0 and implies m = 0 and if are unknown additive mappings satisfying then E and F can be represented by double centralizers. The obtained result implies that one of the equations in the definition of a Jordan *-derivation pair is redundant. Furthermore, a remark on the extension of this result to unknown additive mappings such that is given in a special case.     

Homogeneous algebraic varieties defined by Jordan pairs

Every Jordan pair defines an algebraic varietyX containing as a dense open subset.X is projective (affine) if and only if is separable (radical). The Picard group ofX is generated by the irreducible factors of the generic norm of . If is separable then the automorphism group ofX is the projective group of .