Loop Groups and Twin Buildings

Abstract

In these notes we describe some buildings related to complex Kac–Moody groups. First we describe the spherical building of SLn(ℂ) (i.e. the projective geometry PG(ℂn)) and its Veronese representation. Next we recall the construction of the affine building associated to a discrete valuation on the rational function field ℂ(z). Then we describe the same building in terms of complex Laurent polynomials, and introduce the Veronese representation, which is an equivariant embedding of the building into an affine Kac–Moody algebra. Next, we introduce topological twin buildings. These buildings can be used for a proof which is a variant of the proof by Quillen and Mitchell, of Bott periodicity which uses only topological geometry. At the end we indicate very briefly that the whole process works also for affine real almost split Kac–Moody groups.