Cocompact lattices in locally pro- -complete rank-2 Kac-Moody groups

Abstract

Abstract We initiate an investigation of lattices in a new class of locally compact groups: so-called locally pro- -complete Kac-Moody groups. We discover that in rank 2 their cocompact lattices are particularly well- behaved: under mild assumptions, a cocompact lattice in this completion contains no elements of order . This statement is still an open question for the Caprace-Rémy-Ronan completion. Using this, modulo results of Capdeboscq and Thomas, we classify edge-transitive cocompact lattices and describe a cocompact lattice of minimal covolume. Bibliography: 22 titles.