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Sharp restricted weak-type estimates for sparse operators

Irina Holmes Fay, Guillermo Rey, Kristina Ana Škreb

Abstract

We find the exact Bellman function associated to the level-sets of sparse operators acting on characteristic functions.

Sharp restricted weak-type estimates for sparse operators

Abstract

We find the exact Bellman function associated to the level-sets of sparse operators acting on characteristic functions.
Paper Structure (7 sections, 20 theorems, 194 equations, 19 figures)

This paper contains 7 sections, 20 theorems, 194 equations, 19 figures.

Key Result

Corollary 1

If $\mathcal{S}$ is sparse, $E \subseteq [0,1)$, $|E| = 2^{-n}$, and $\lambda \in \mathbb{N} - 2^{-n}$ is at least $2$, then and equality is attained for certain pairs $(E, \mathcal{S})$.

Figures (19)

  • Figure 1: $(x, A)$-domain regions for $0<\lambda\leq 1$
  • Figure 2: Diagram of $\mathbf{f}$. Here $C$ and $D$ represent the two possible positions of the point $(x_\ast, \lambda_\ast)$.
  • Figure 3: Concatenation of $\alpha$ and $\beta$, assigning $\gamma$ to the top interval. Here $I = [0,1)$ and the suffix $+$ or $-$ denotes the right or left child respectively.
  • Figure 4: Inductive application of \ref{['construction:x=1']} to obtain \ref{['construction:x=1:full']}.
  • Figure 5: Lower bounds for $\mathbb{F}$. The green line is given by Proposition \ref{['construction:first_nontrivial']}, and the red is obtained by applying \ref{['construction:C']} and \ref{['bellman:jump']}.
  • ...and 14 more figures

Theorems & Definitions (37)

  • Corollary
  • Theorem A
  • Theorem 2.1
  • proof
  • Definition 2.1
  • Definition 2.2
  • Theorem 2.2
  • proof
  • Theorem 2.3
  • proof
  • ...and 27 more