arXiv subjects

Luca Haardt

Publications and source records attributed to Luca Haardt.

4 recordsLinked to original sources

arXiv2026

On the $\mathrm{L}^p$-theory of the generalized Stokes operator with rough coefficients

In this article, we establish $\mathrm{L}^p$-mapping properties for the generalized Stokes operator with bounded measurable coefficients on the full range of exponents that is known to be sharp for elliptic systems with rough coefficients. These include $\mathrm{L}^p$-estimates for the corresponding semigroup, its gradient and the $\mathrm{H}^\infty$-calculus, as well as $\mathrm{L}^q$-$\mathrm{L}^p$ smoothing estimates. As a key ingredient, we develop an abstract framework that captures the relationship between hypercontractivity, non-local decay estimates and uniform $\L^p$-bounds.

math.AP↗

arXiv2026

A coherent theory of tent spaces and homogeneous Triebel-Lizorkin spaces

We introduce and systematically investigate a scale of tent spaces that characterizes homogeneous Triebel-Lizorkin spaces $\mathrm{\dot F}^{\beta}_{p,q}$. These spaces generalize the classical spaces of Coifman, Meyer, and Stein, and are shown to be equivalent to the weighted tent spaces with Whitney averages developed by Huang. We show that these tent spaces follow a functional analytic theory that mirrors that of Triebel-Lizorkin spaces, including duality, embeddings, discrete characterizations, John-Nirenberg-type properties, as well as real and complex interpolation. Furthermore, we provide a novel characterization of the endpoint spaces $\mathrm{\dot F}^\beta_{\infty,q}$, completing earlier work by Auscher, Bechtel, and the author.

math.CA↗

arXiv2025

A new scale of function spaces characterizing homogeneous Besov spaces

We introduce and study a new scale of function spaces that characterize the homogeneous Besov spaces $\mathrm{\dot B}^{\beta}_{p,q}$, hence completing earlier work by Ullrich. These new spaces include the ones introduced by Barton and Mayboroda, and systematically studied by Amenta under the name of weighted $\mathrm{Z}$-spaces, for the purpose of boundary value problems with $\mathrm{\dot B}^{\beta}_{p,p}$ data. They are the counterparts to the weighted tent spaces with Whitney averages, developed by Huang, and arise as their real interpolants. We describe their functional analytic properties: completeness, duality, embeddings, as well as their real and complex interpolants.

math.CA↗

arXiv2024

On Kato's Square Root Property for the Generalized Stokes Operator

We establish the Kato square root property for the generalized Stokes operator on $\mathbb{R}^d$ with bounded measurable coefficients. More precisely, we identify the domain of the square root of $Au := - \operatorname{div}(\mu \nabla u) + \nabla \phi$, $\operatorname{div}(u) = 0$, with the space of divergence-free $\mathrm{H}^1$-vector fields and further prove the estimate $\|A^{1/2} u \|_{\mathrm{L}^2} \simeq \| \nabla u \|_{\mathrm{L}^2}$. As an application we show that $A^{1/2}$ depends holomorphically on the coefficients $\mu$. Besides the boundedness and measurablility as well as an ellipticity condition on $\mu$, there are no requirements on the coefficients.

math.AP↗