On the l^2-Betti numbers of universal quantum groups
  We show that the first $\ell^2$-Betti number of the duals of the free unitary quantum groups is one, and that all $\ell^2$-Betti numbers vanish for the duals of the quantum automorphism groups of full matrix algebras. 
David Kyed, Sven Raum
math.OA