Wonderful Compactification of Character Varieties

Indranil Biswas, Sean Lawton, Daniel Ramras

Published 2017-03-13Version 1

Using the wonderful compactification of a semisimple adjoint affine algebraic group G defined over an algebraically closed field k of arbitrary characteristic, we construct a natural compactification Y of the G-character variety of any finitely generated group F. When F is a free group, we show that this compactification is always simply connected with respect to the \'etale fundamental group, and when k=C it is also topologically simply connected. For other groups F, we describe conditions for the compactification of the moduli space to be simply connected and give examples when these conditions are satisfied, including closed surface groups and free abelian groups when G=PGL(n,C). Additionally, when F is free we identify the boundary divisors of Y in terms of previously studied moduli spaces, and we construct a Poisson structure on Y and its boundary divisors.