The families of orthogonal, unitary and quaternionic unitary Cayley--Klein algebras and their central extensions

Abstract

The families of quasi-simple or Cayley--Klein algebras associated to antihermitian matrices over R, C and H are described in a unified framework. These three families include simple and non-simple real Lie algebras which can be obtained by contracting the pseudo-orthogonal algebras so(p,q) of the Cartan series $B_l$ and $D_l$, the special pseudo-unitary algebras su(p,q) in the series $A_l$, and the quaternionic pseudo-unitary algebras sq(p,q) in the series $C_l$. This approach allows to study many properties for all these Lie algebras simultaneously. In particular their non-trivial central extensions are completely determined in arbitrary dimension.

10 pages, LaTeX. Contribution to the III Classical and Quantum Integrable Systems. Edited by L.G. Mardoyan, G.S. Pogosyan and A.N. Sissakian. JINR, Dubna, pp. 58--67, (1998)