Weighted Inequalities for the Fractional Laplacian and the Existence of Extremals

Abstract

In this article we obtain improved versions of Stein-Weiss and Caffarelli-Kohn-Nirenberg inequalities, involving Besov norms of negative smoothness. As an application of the former, we derive the existence of extremals of the Stein-Weiss inequality in certain cases, some of which are not contained in the celebrated theorem of E. Lieb.

20 pages; added references, corrected typos, and other minor changes