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Quantitative formulations of Feffermans counterexample for the ball multiplier are naturally linked to square function and vector-valued estimates for directional singular integrals. The latter are usually referred to as Meyer-type lemmas and are traditionally attacked by combining weighted inequalities with sharp estimates for maximal directional averaging operators. This classical approach fails to give sharp bounds. In this article we develop a novel framework for square function estimates, based on directional Carleson embedding theorems and multi-parameter time-frequency analysis, which overcomes the limitations of weighted theory. In particular we prove the sharp form of Meyers lemma, namely a sharp operator norm bound for vector-valued directional singular integrals, in both one and two parameters, in terms of the cardinality of the given set of directions. Our sharp Meyer lemma implies an improved quantification of the reverse square function estimate for tangential $deltatimes delta^2$-caps on $mathbb S^1$. We also prove sharp square function estimates for conical and radial multipliers. A suitable combination of these estimates yields a new and currently best known bound for the Fourier restriction to a $N$-gon, improving on previous results of A. Cordoba.
In this paper, we prove a sharp Meis Lemma with assuming the bases of the underlying general dyadic grids are different. As a byproduct, we specify all the possible cases of adjacent general dyadic systems with different bases. The proofs have connections with certain number-theoretic properties.
Using the Fourier analysis techniques on hyperbolic spaces and Greens function estimates, we confirm in this paper the conjecture given by the same authors in [43]. Namely, we prove that the sharp constant in the $frac{n-1}{2}$-th order Hardy-Sobolev
In this note, we prove the sharp Davies-Gaffney-Grigoryan lemma for minimal heat kernels on graphs.
We consider 2d critical Bernoulli percolation on the square lattice. We prove an approximate color-switching lemma comparing k arm probabilities for different polychromatic color sequences. This result is well-known for site percolation on the triang
We provide elementary proofs for the terms that are left in the work of Kelly Bickel, Sandra Pott, Maria C. Reguera, Eric T. Sawyer, Brett D. Wick who proved the sharp weighted $A_2$ bound for Haar shifts and Haar multiplier. Our proofs use weighted