  We prove two results about the natural representation of a group G of
automorphisms of a normal projective threefold X on its second cohomology. We
show that if X is minimal then G, modulo a normal subgroup of null entropy, is
embedded as a Zariski-dense subset in a semi-simple real linear algebraic group
of real rank < 3. Next, we show that X is a complex torus if the image of G is
an almost abelian group of positive rank and the kernel is infinite, unless X
is equivariantly non-trivially fibred.
