Spin covers of maximal compact subgroups of Kac-Moody groups and of Weyl groups

The maximal compact subgroup SO(\(n\),ℝ) of SL(\(n\),ℝ) admits two double covers Spin (\(n\),ℝ) and O(\(n\),ℝ). In this thesis we show that in fact given any simply-laced diagram ∆, with associated split real Kac-Moody group \(G\)(∆), the 'maximal compact' subgroup \(K\)(∆)also admits a double cover Spin(∆). We then describe a subgroup of Spin(∆) which is a cover of the Weyl group \(W\)(∆) associated to g(∆). This answers a conjecture of Damour and Hillmann. Moreover, the group \(D\) which extends \(W\) is used in an attempt to classify the images of the so-called generalised spin representations