Jean Dolbeault, Ari Laptev, and Michael Loss Lieb-Thirring inequalities with improved constants (15K, LaTeX) ABSTRACT. Following Eden and Foias we obtain a matrix version of a generalised Sobolev inequality in one-dimension. This allow us to improve on the known estimates of best constants in Lieb-Thirring inequalities for the sum of the negative eigenvalues for multi-dimensional Schroedinger operators.