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Mario Milman

Publications and source records attributed to Mario Milman.

At least 19 recordsLinked to original sources
arXiv2023

A sharp stability criterion for Euler equations via sparseness

We introduce sparse versions of function spaces that are relevant to characterize the solutions of Euler equations without concentration. The standard Sobolev space $H^{-1}$ is given a sparse structure that allows to measure the degree of compactness of embeddings into $H^{-1}$ and provides new quantitative general criteria for $H^{-1}$-stability. Indices of sparseness are defined, and function spaces whose indices have prescribed decay are constructed, resulting in an improvement of the classical $H^{-1}$-stability results: sparse stability. The analysis relies on the introduction of sparse Riesz-Morrey-Tadmor spaces, that are characterized via maximal operators and new sparse domination theorems, together with extrapolation techniques. Our methods also yield improvements on recent results on the conservation of energy of physically realizable solutions of $2$D-Euler.

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arXiv2023

Uniqueness for 2D Euler and transport equations via extrapolation

Using extrapolation theory, we develop a new framework to prove the uniqueness of solutions for transport equations. We apply our methodology to unify and extend the classical results of Yudovich and Vishik for 2D Euler equations. In particular, we establish the uniqueness for the Euler flow whose vorticity belongs to new scales of function spaces that contain both Yudovich spaces and BMO. We give a self contained presentation.

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arXiv2021

Bourgain-Brezis-Mironescu-Maz'ya-Shaposhnikova limit formulae for fractional Sobolev spaces via interpolation and extrapolation

The real interpolation spaces between $L^{p}({\mathbb{R}}^{n})$ and $\dot {H}^{t,p}({\mathbb{R}}^{n})$ (resp. $H^{t,p}({\mathbb{R}}^{n})$), $t>0,$ are characterized in terms of fractional moduli of smoothness, and the underlying seminorms are shown to be " the correct" fractional generalization of the classical Gagliardo seminorms. This is confirmed by the fact that, using the new spaces combined with interpolation and extrapolation methods, we are able to extend the Bourgain-Brezis-Mironescu-Maz'ya-Shaposhnikova limit formulae, as well as the Bourgain-Brezis-Mironescu convergence theorem, to fractional Sobolev spaces. On the other hand, we disprove a conjecture of \cite{Braz} suggesting fractional convergence results given in terms of classical Gagliardo seminorms. We also solve a problem proposed in \cite{Braz} concerning sharp forms of the fractional Sobolev embedding.

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arXiv2021

Majorization revisited: Comparison of norms in interpolation scales

We reformulate, modify and extend a comparison criteria of $L^{p}$ norms obtained by Nazarov-Podkorytov and place it in the general setting of interpolation theory and majorization theory. In particular, we give norm comparison criteria for general scales of interpolation spaces, including non-commutative $L^{p}$ and Lorentz spaces. As an application, we extend the classical Ball's integral inequality, which lies at the basis of his famous result on sections of the $n-$dimensional unit cube.

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arXiv2021

Sparse Brudnyi and John-Nirenberg Spaces

A generalization of the theory of Y. Brudnyi \cite{yuri}, and A. and Y. Brudnyi \cite{BB20a}, \cite{BB20b}, is presented. Our construction connects Brudnyi's theory, which relies on local polynomial approximation, with new results on sparse domination. In particular, we find an analogue of the maximal theorem for the fractional maximal function, solving a problem proposed by Kruglyak--Kuznetsov. Our spaces shed light on the structure of the John--Nirenberg spaces. We show that $SJN_{p}$ (sparse John--Nirenberg space) coincides with $L^{p},1<p<\infty.$ This characterization yields the John--Nirenberg inequality by extrapolation and is useful in the theory of commutators.

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arXiv2020

New Brezis-Van Schaftingen-Yung Sobolev type inequalities connected with maximal inequalities and one parameter families of operators

Motivated by the recent characterization of Sobolev spaces due to Brezis-Van Schaftingen-Yung we prove new weak-type inequalities for one parameter families of operators connected with mixed norm inequalities. The novelty here comes from the fact that the underlying measure space incorporates the parameter as a variable. The connection to classical and fractional order Sobolev spaces is shown through the use of generalized Riesz potential spaces and the Caffarelli-Silvestre extension principle. Higher order inequalities are also considered. We indicate many examples and applications to PDE's and different areas of Analysis, suggesting a vast potential for future research. In a different direction, and inspired by methods originally due to Gagliardo and Garsia, we obtain new maximal inequalities which combined with mixed norm inequalities are applied to obtain Brezis--Van Schaftingen--Yung type inequalities in the context of Calder\'{o}n-Campanato spaces. In particular, Log versions of the Gagliardo-Brezis-Van Schaftingen-Yung spaces are introduced and \ compared with corresponding limiting versions of Calder\'{o}n-Campanato spaces, resulting in a sharpening of recent inequalities due to Crippa-De Lellis and Bru\'{e}-Nguyen.

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arXiv2019

Reverse Holder inequalities revisited: Interpolation, Extrapolation, Indices and Doubling

Extending results in \cite{M} and \cite{MM} we characterize the classical classes of weights that satisfy reverse H\"{o}lder inequalities in terms of indices of suitable families of $K-$functionals of the weights. In particular, we introduce a Samko type of index (cf. \cite{kara}) for families of functions, that is based on quasi-monotonicity, and use it to provide an index characterization of the $RH_{p}$ classes, as well as the limiting class $RH=$ $RH_{LLogL}=$. $\bigcup\limits_{p>1}RH_{p}$ (cf. \cite{BMR}),\ which in the abstract case involves extrapolation spaces. Reverse H\"{o}lder inequalities associated to $L(p,q)$ norms, and non-doubling measures are also treated.

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arXiv2018

Limiting interpolation spaces via extrapolation

We give a complete characterization of limiting interpolation spa\-ces for the real method of interpolation using extrapolation theory. For this purpose the usual tools (e.g., Boyd indices or the boundedness of Hardy type operators) are not appropriate. Instead, our characterization hinges upon the boundedness of some simple operators (e.g. $f\mapsto f(t^{2})/t$, or $f\mapsto f(t^{1/2}% )$) acting on the underlying lattices that are used to control the $K$- and $J$-functionals. Reiteration formulae, extending Holmstedt's classical reiteration theorem to limiting spaces, are also proved and characterized in this fashion. The resulting theory gives a unified roof to a large body of literature that, using ad-hoc methods, had covered only special cases of the results obtained here. Applications to Matsaev ideals, Grand Lebesgue spaces, Bourgain-Brezis-Mironescu-Maz'ya-Shaposhnikova limits, as well as a new vector valued extrapolation theorems, are provided.

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arXiv2017

Garsia-Rodemich spaces: Local Maximal Functions and Interpolation

We characterize the Garsia-Rodemich spaces associated with a rearrangement invariant space via local maximal operators. Let $Q_{0}$ be a cube in $R^{n}$. We show that there exists $s_{0}\in(0,1),$ such that for all $0<s<s_{0},$ and for all r.i. spaces $X(Q_{0}),$ we have% \[ GaRo_{X}(Q_{0})=\{f\in L^{1}(Q_{0}):\Vert f\Vert_{GaRo_{X}}\simeq\Vert M_{0,s,Q_{0}}^{\#}f\Vert_{X}<\infty\}, \] where $M_{0,s,Q_{0}}^{\#}$ is the Str\"{o}mberg-Jawerth-Torchinsky local maximal operator. Combined with a formula for the $K-$functional of the pair $(L^{1},BMO)$ obtained by Jawerth-Torchinsky, our result shows that the $GaRo_{X}$ spaces are interpolation spaces between $L^{1}$ and $BMO.$ Among the applications, we prove, using real interpolation, the monotonicity under rearrangements of Garsia-Rodemich type functionals. We also give an approach to Sobolev-Morrey inequalities via Garsia-Rodemich norms, and prove necessary and sufficient conditions for $GaRo_{X}(Q_{0})=X(Q_{0}).$ Using packings, we obtain a new expression for the $K-$functional of the pair $(L^{1},BMO)$.

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arXiv2016

Garsia-Rodemich Spaces: Bourgain-Brezis-Mironescu space, embeddings and rearrangement invariant spaces

We extend the construction of Garsia-Rodemich spaces in different directions. We show that the new space \textbf{B,} introduced by Bourgain-Brezis-Mironescu \cite{bbm}, can be described via a suitable scaling of the Garsia-Rodemich norms. As an application we give a new proof of the embeddings $BMO\subset$ \textbf{B }$\subset$ $L(n^{\prime},\infty).$ We then generalize the Garsia-Rodemich construction and introduce the $GaRo_{X}$ spaces associated with a rearrangement invariant space $X,$ in such a way that $GaRo_{X}=X,$ for a large class of rearrangement invariant spaces. The underlying inequality for this new characterization of rearrangement invariant spaces is an extension of the rearrangement inequalities of \cite{milbmo}. We introduce Gagliardo seminorms adapted to rearrangement invariant spaces and use our generalized Garsia-Rodemich construction to prove Fractional Sobolev inequalities in this context.

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arXiv2015

Marcinkiewicz spaces, Garsia-Rodemich spaces and the scale of John-Nirenberg self improving inequalities

We extend to n-dimensions a characterization of the Marcinkiewicz $L(p,\infty)$ spaces first obtained by Garsia-Rodemich in the one dimensional case. This leads to a new proof of the John-Nirenberg self-improving inequalities. We also show a related result that provides a still a new characterization of the $L(p,\infty)$ spaces in terms of distribution functions, reflects the self-improving inequalities directly, and also characterizes $L(\infty,\infty),$ the rearrangement invariant hull of $BMO.$ We show an application to the study of tensor products with $L(\infty,\infty)$ spaces, which complements the classical work of O'Neil \cite{oneil} and the more recent work of Astashkin \cite{astashkin}.

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arXiv2015

The $\infty$-Besov Capacity Problem

A theory of $\infty$-Besov capacities is developed and several applications are provided. In particular, we solve an open problem in the theory of limits of the $\infty$-Besov semi-norms, we obtain new restriction-extension inequalities and we characterize the point-wise multipliers acting on the $\infty$-Besov spaces.

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arXiv2015

Isoperimetric weights and generalized uncertainty inequalities in metric measure spaces

We extend the recent $L^{1}$ uncertainty inequalities obtained by Dall'ara-Trevisan to the metric setting. For this purpose we introduce a new class of weights, named *isoperimetric weights*, for which the growth of the measure of their level sets $\mu(\{w\leq r\})$ can be controlled by $rI(r),$ where $I$ is the isoperimetric profile of the ambient metric space. We use isoperimetric weights, new *localized Poincar\'e inequalities*, and interpolation, to prove $L^{p},1\leq p<\infty,$ uncertainty inequalities on metric measure spaces. We give an alternate characterization of the class of isoperimetric weights in terms of Marcinkiewicz spaces, which combined with the sharp Sobolev inequalities we had obtained in an earlier paper, and interpolation of weighted norm inequalities, give new uncertainty inequalities in the context of rearrangement invariant spaces.

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arXiv2014

A brief survey of Nigel Kalton's work on interpolation and related topics

This is the third of a series of papers surveying some small part of the remarkable work of our friend and colleague Nigel Kalton. We have written it as part of a tribute to his memory. It does not contain new results. This time, rather than concentrating on one particular paper, we attempt to give a general overview of Nigel's many contributions to the theory of interpolation of Banach spaces, and also, significantly, quasi-Banach spaces.

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