Uniqueness of quasi-Einstein metrics on 3-dimensional homogeneous   manifolds
  The purpose of this article is to study the existence and uniqueness of quasi-Einstein structures on $3$-dimensional homogeneous Riemannian manifolds. To this end, we use the eight model geometries for 3-dimensional manifolds identified by Thurston. First, we present here a complete description of quasi-Einstein metrics on $3$-dimensional homogeneous manifolds with isometry group of dimension $4.$ In addition, we shall show the absence of such gradient structure on $Sol^3,$ which has $3$-dimensional isometry group. Moreover, we prove that Berger's spheres carry a non-trivial quasi-Einstein structure with non gradient associated vector field, this shows that a theorem due to Perelman can not be extend to quasi-Einstein metrics. Finally, we prove that a $3$-dimensional homogeneous manifold carrying a gradient quasi-Einstein structure is either Einstein or $\mathbb{H}^2_{\kappa} \times \mathbb{R}.$ 
A. Barros, E. Ribeiro Jr and J. Silva Filho
math.DG