No Arabic abstract
Let $M = mathbb R^m sharp mathcal R^n$ be a non-doubling manifold with two ends $mathbb R^m sharp mathcal R^n$, $m > n ge 3$. Let $Delta$ be the Laplace--Beltrami operator which is non-negative self-adjoint on $L^2(M)$. Then $Delta$ and its square root $sqrt{Delta}$ generate the semigroups $e^{-tDelta}$ and $e^{-tsqrt{Delta}}$ on $L^2(M)$, respectively. We give testing conditions for the two weight inequality for the Poisson semigroup $e^{-tsqrt{Delta}}$ to hold in this setting. In particular, we prove that for a measure $mu$ on $M_{+}:=Mtimes (0,infty)$ and $sigma$ on $M$: $$ |mathsf{P}_sigma(f)|_{L^2(M_{+};mu)} lesssim |f|_{L^2(M;sigma)}, $$ with $mathsf{P}_sigma(f)(x,t):= int_M mathsf{P}_t(x,y)f(y) ,dsigma(y)$ if and only if testing conditions hold for the Poisson semigroup and its adjoint. Further, the norm of the operator is shown to be equivalent to the best constant in these testing conditions.
For the maximal operator $ M $ on $ mathbb R ^{d}$, and $ 1< p , rho < infty $, there is a finite constant $ D = D _{p, rho }$ so that this holds. For all weights $ w, sigma $ on $ mathbb R ^{d}$, the operator $ M (sigma cdot )$ is bounded from $ L ^{p} (sigma ) to L ^{p} (w)$ if and only the pair of weights $ (w, sigma )$ satisfy the two weight $ A _{p}$ condition, and this testing inequality holds: begin{equation*} int _{Q} M (sigma mathbf 1_{Q} ) ^{p} ; d w lesssim sigma ( Q), end{equation*} for all cubes $ Q$ for which there is a cube $ P supset Q$ satisfying $ sigma (P) < D sigma (Q)$, and $ ell P = rho ell Q$. This was recently proved by Kangwei Li and Eric Sawyer. We give a short proof, which is easily seen to hold for several closely related operators.
We study the Rellich inequalities in the framework of equalities. We present equalities which imply the Rellich inequalities by dropping remainders. This provides a simple and direct understanding of the Rellich inequalities as well as the nonexistence of nontrivial extremisers.
One may define a trilinear convolution form on the sphere involving two functions on the sphere and a monotonic function on the interval $[-1,1]$. A symmetrization inequality of Baernstein and Taylor states that this form is maximized when the two functions on the sphere are replaced with their nondecreasing symmetric rearrangements. In the case of indicator functions, we show that under natural hypotheses, the symmetric rearrangements are the only maximizers up to symmetry by establishing a sharpened inequality.
This paper is a companion to our prior paper arXiv:0705.4619 on the `Small Ball Inequality in All Dimensions. In it, we address a more restrictive inequality, and obtain a non-trivial, explicit bound, using a single essential estimate from our prior paper. The prior bound was not explicit and much more involved.
This paper gives new two-weight bump conditions for the sparse operators related to iterated commutators of fractional integrals. As applications, the two-weight bounds for iterated commutators of fractional integrals under more general bump conditions are obtained. Meanwhile, the necessity of two-weight bump conditions as well as the converse of Bloom type estimates for iterated commutators of fractional integrals are also given.