Pitt's inequality with sharp convolution estimates
  Sharp $L^p$ extensions of Pitt's inequality expressed as a weighted Sobolev inequality are obtained using convolution estimates and Stein-Weiss potentials. More generally, optimal constants are obtained for the full Stein-Weiss potential as a map from $L^p$ to itself, and new proofs are given for the classical Pitt and Stein-Weiss estimates. 
William Beckner