On sharp constants in higher order Adams-Cianchi inequalities

The main results of this paper are the establishment of sharp constants for several families of critical Sobolev embeddings. These inequalities were pioneered by David R. Adams, while the sharp constant in the first order case is due to Andrea Cianchi. We also prove a trace improvement of an inequality obtained independently by K. Hansson and H. Brezis and S. Wainger.