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Equivalence of Sobolev norms for Kolmogorov operators with scaling-critical drift

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Published 21 January 2026 © 2026 The Author(s). Published by IOP Publishing Ltd and the London Mathematical Society.
, , Citation The Anh Bui et al 2026 Nonlinearity 39 015021DOI 10.1088/1361-6544/ae277a

0951-7715/39/1/015021

Abstract

We consider the ordinary or fractional Laplacian plus a homogeneous, scaling-critical drift term. This operator is non-symmetric but homogeneous, and generates scales of Lp-Sobolev spaces which we compare with the ordinary homogeneous Sobolev spaces. Unlike in previous studies concerning Hardy operators, i.e. ordinary or fractional Laplacians plus scaling-critical scalar perturbations, handling the drift term requires an additional, possibly technical, restriction on the range of comparable Sobolev spaces, which is related to the unavailability of gradient bounds for the associated semigroup.

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Footnotes

  • See also [KPS81, Yaf99, FLS08, FS08] for other proofs of (1.3) with the optimal constant $\kappa_*$. Formula (1.3) is often simply called Hardy inequality.

  • While [KS20, KSS21, KS23] state their results only for $d\in\{3,4,\ldots\}$ and $\alpha\in(1,2]$, an inspection of their proofs, taking (1.11) into account, show that all their results actually hold for all $d\in\mathbb{N}$ and $\alpha\in(1,2]$ with $\alpha \lt (d+2)/2$.

  • We point out two misprints in [BD23, (3)]: There, the operators $(-\Delta)^{\alpha s/2}$ and $(\mathcal{L}_a)^{\alpha s/4}$ should be replaced with $(-\Delta)^{\alpha s/4}$ and $(\mathcal{L}_a)^{s/2}$, respectively.

  • For single or finitely many eigenvalues, this is known as Feynman–Hellmann theorem.

  • Actually, one has to show this relative trace class condition only in every fixed angular momentum channel, i.e. when the operator is restricted to the space of square-integrable functions of the form $f(|x|)Y_\ell(x/|x|)$, where $Y_\ell$ denotes the $\ell$-th spherical harmonic on the unit sphere.

  • See [Azi69] for a reprint of [McK67].

  • 10 

    The terminologies ‘supercritical’ and ‘critical’ are motivated by the fact that a gradient perturbation $b\cdot\nabla$ is of the same weight as $\sqrt{-\Delta}$, while if α < 1, then, formally, $b\cdot\nabla$ dominates $(-\Delta)^{\alpha/2}$.

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