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Maximal representations of uniform complex hyperbolic lattices

Let $ρ$ be a maximal representation of a uniform lattice $Γ\subset{\rm SU}(n,1)$, $n\geq 2$, in a classical Lie group of Hermitian type $H$. We prove that necessarily $H={\rm SU}(p,q)$ with $p\geq qn$ and there exists a holomorphic or antiholomorphic $ρ$-equivariant map from complex hyperbolic space to the symmetric space associated to ${\rm SU}(p,q)$. This map is moreover a totally geodesic homothetic embedding. In particular, up to a representation in a compact subgroup of ${\rm SU}(p,q)$, the representation $ρ$ extends to a representation of ${\rm SU}(n,1)$ in ${\rm SU}(p,q)$.