Optimal embeddings into Lorentz spaces for some vector differential operators via Gagliardo's lemma

Abstract

We prove a family of Sobolev inequalities of the form parallel to u parallel to(n/Ln-1, 1(Rn, V)) <= C parallel to A(D)u parallel to(L1(Rn,E)) where A(D) : C-c(infinity)(R-n ,V) -> C-c(infinity)(R-n , E) is a vector first-order homogeneous linear differential operator with constant coefficients, a is a vector field on R-n and L-n/n-1,L- 1 (R-n) is a Lorentz space. These new inequalities imply in particular the extension of the classical Gagliardo-Nirenberg inequality to Lorentz spaces originally due to Alvino and a sharpening of an inequality in terms of the deformation operator by Strauss (Korn Sobolev inequality) on the Lorentz scale. The proof relies on a nonorthogonal application of the Loomis-Whitney inequality and Gagliardo's lemma.