Sharp second order uncertainty principles

Abstract

We study sharp second order inequalities of Caffarelli-Kohn-Nirenberg type in the euclidian space ${\mathbb{R}}^N$, where $N$ denotes the dimension. This analysis is equivalent to the study of uncertainty principles for special classes of vector fields. In particular, we show that when switching from scalar fields $u: \rr^n\rightarrow \mathbb{C}$ to vector fields of the form $\vec{u}:=\nabla U$ ($U$ being a scalar field) the best constant in the Heisenberg Uncertainty Principle (HUP) increases from $\frac{N^2}{4}$ to $\frac{(N+2{)}^2}{4}$, and the optimal constant in the Hydrogen Uncertainty Principle (HyUP) improves from $\frac{{\left(N-1\right)}^2}{4}$ to $\frac{(N+1{)}^2}{4}$. As a consequence of our results we answer to the open question of Maz'ya (Integral Equations Operator Theory 2018) in the case $N=2$ regarding the HUP for divergence free vector fields.

25 pages