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Marisa Toschi

Publications and source records attributed to Marisa Toschi.

6 recordsLinked to original sources

A $T1$ criterion for Schr\"odinger-Calder\'on-Zygmund operators with exponential decay

We establish the boundedness of exponential Schr\"odinger-Calder\'on-Zygmund operators on weighted $BMO_\rho^\alpha(w)$ spaces via a $T1$ criterion, where the weights belong to classes that capture the exponential decay of the operators, and $\rho$ is a critical radius function. Specifically, we prove that the boundedness of such an operator $T$ on $BMO_\rho^\alpha(w)$ is equivalent to a natural oscillation condition on $T1$ over sub-critical balls. The weight classes considered, introduced in connection with $\rho$, include and extend the classical $A_p^\rho$ weights, and are well-adapted to the exponential decay of the kernels. As applications, we derive weighted endpoint estimates for several operators associated to the generalized Schr\"odinger operator $\mathcal{L}_\mu=-\Delta+\mu$, including Riesz transforms, Laplace transform-type multipliers, maximal operators for the heat and Poisson semigroups, Littlewood-Paley functions and fractional integral operators. When $d\mu(x)=V(x)dx$, the results above extend the known endpoint estimates to larger classes of weights.

math.AP

Weighted estimates for Schr\"odinger-Calder\'on-Zygmund operators with exponential decay

In this work we obtain weighted boundedness results for singular integral operators with kernels exhibiting exponential decay. We also show that the classes of weights are characterized by a suitable maximal operator. Additionally, we study the boundedness of various operators associated with the generalized Schr\"odinger operator $-\Delta + \mu$, where $\mu$ is a nonnegative Radon measure in $\mathbb{R}^d$, for $d\geq 3$.

math.AP

The sharp maximal function approach to $L^{p}$ estimates for operators structured on Hörmander's vector fields

We consider a nonvariational degenerate elliptic operator structured on a system of left invariant, 1-homogeneous, Hörmander's vector fields on a Carnot group in $R^{n}$, where the matrix of coefficients is symmetric, uniformly positive on a bounded domain of $R^{n}$ and the coefficients are bounded, measurable and locally VMO in the domain. We give a new proof of the interior $L^{p}$ estimates on the second order derivatives with respect to the vector fields, first proved by Bramanti-Brandolini in [Rend. Sem. Mat. dell'Univ. e del Politec. di Torino, Vol. 58, 4 (2000), 389-433], extending to this context Krylov' technique, introduced in [Comm. in P.D.E.s, 32 (2007), 453-475], consisting in estimating the sharp maximal function of the second order derivatives.

math.AP

On s-sets in spaces of homogeneous type

Let $(X,d,μ)$ be a space of homogeneous type. In this note we study the relationship between two types of $s$-sets: relative to a distance and relative to a measure. We find a condition on a closed subset $F$ of $X$ under which we have that $F$ is $s$-set relative to the measure $μ$ if and only if $F$ is $s$-set relative to $δ$. Here $δ$ denotes the quasi-distance defined by Macías and Segovia such that $(X,δ,μ)$ is a normal space. In order to prove this result, we show a covering type lemma and a type of Hausdorff measure based criteria for the $s$-set condition relative to $μ$ of a given set.

math.MG

Powers of distances to lower dimensional sets as Muckenhoupt weights

Let $(X,d,μ)$ be an Ahlfors metric measure space. We give sufficient conditions on a closed set $F\subseteq X$ and on a real number $β$ in such a way that $d(x,F)^β$ becomes a Muckenhoupt weight. We give also some illustrations to regularity of solutions of partial differential equations and regarding some classical fractals.

math.FA

On the existence of bounded solutions for a nonlinear elliptic system

This work deals with the system $(-Δ)^m u= a(x) v^p$, $(-Δ)^m v=b(x) u^q$ with Dirichlet boundary condition in a domain $Ω\subset\RR^n$, where $Ω$ is a ball if $n\ge 3$ or a smooth perturbation of a ball when $n=2$. We prove that, under appropriate conditions on the parameters ($a,b,p,q,m,n$), any non-negative solution $(u,v)$ of the system is bounded by a constant independent of $(u,v)$. Moreover, we prove that the conditions are sharp in the sense that, up to some border case, the relation on the parameters are also necessary. The case $m=1$ was considered by Souplet in \cite{PS}. Our paper generalize to $m\ge 1$ the results of that paper.

math.AP