Sharp Gagliardo-Nirenberg inequalities in fractional Coulomb-Sobolev spaces

Abstract

We prove scaling invariant Gagliardo-Nirenberg type inequalities of the form $$\|φ\|_{L^p(\mathbb{R}^d)}\le C\|φ\|_{\dot H^{s}(\mathbb{R}^d)}^β \left(\iint_{\mathbb{R}^d \times \mathbb{R}^d} \frac{|φ(x)|^q\,|φ(y)|^q}{|x - y|^{d-α}} dx dy\right)^γ,$$ involving fractional Sobolev norms with $s>0$ and Coulomb type energies with $0<α<d$ and $q\ge 1$. We establish optimal ranges of parameters for the validity of such inequalities and discuss the existence of the optimisers. In the special case $p=\frac{2d}{d-2s}$ our results include a new refinement of the fractional Sobolev inequality by a Coulomb term. We also prove that if the radial symmetry is taken into account, then the ranges of validity of the inequalities could be extended and such a radial improvement is possible if and only if $α>1$.

27 pages, introduction and references updated