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Carme Cascante

Publications and source records attributed to Carme Cascante.

14 recordsLinked to original sources
arXiv2025

Composition of analytic paraproducts

For a fixed analytic function $g$ on the unit disc $\mathbb{D}$, we consider the analytic paraproducts induced by $g$, which are defined by $T_gf(z)= \int_0^z f(ζ)g'(ζ)\,dζ$, $S_gf(z)= \int_0^z f'(ζ)g(ζ)\,dζ$, and $M_gf(z)= f(z)g(z)$. The boundedness of these operators on various spaces of analytic functions on $\mathbb{D}$ is well understood. The original motivation for this work is to understand the boundedness of compositions of two of these operators, for example $T_g^2, \,T_gS_g,\, M_gT_g$, etc. Our methods yield a characterization of the boundedness of a large class of operators contained in the algebra generated by these analytic paraproducts acting on the classical weighted Bergman and Hardy spaces in terms of the symbol $g$. In some cases it turns out that this property is not affected by cancellation, while in others it requires stronger and more subtle restrictions on the oscillation of the symbol $g$ than the case of a single paraproduct.

math.CV↗
arXiv2023

Words of analytic paraproducts on Hardy and weighted Bergman spaces

For a fixed analytic function g on the unit disc, we consider the analytic paraproducts induced by g, which are formally defined by $T_gf(z)=\int_0^zf(ζ)g'(ζ)dζ$, $S_gf(z)=\int_0^zf'(ζ)g(ζ)dζ$, and $M_gf(z)=g(z)f(z)$. We are concerned with the study of the boundedness of operators in the algebra $\mathcal{A}_g$ generated by the above operators acting on Hardy, or standard weighted Bergman spaces on the disc. The general question is certainly very challenging, since operators in $\mathcal{A}_g$ are finite linear combinations of finite products (words) of $T_g,S_g,M_g$ which may involve a large amount of cancellations to be understood. The results in the paper "Composition of analytic paraproducts, J. Math. Pures Appl. 158 (2022) 293--319" show that boundedness of operators in a fairly large subclass of $\mathcal{A}_g$ can be characterized by one of the conditions $g\in H^\infty$, or $g^n$ belongs to $BMOA$ or the Bloch space, for some integer $n>0$. However, it is also proved that there are many operators, even single words in $\mathcal{A}_g$ whose boundedness cannot be described in terms of these conditions. The present paper provides a considerable progress in this direction. Our main result provides a complete quantitative characterization of the boundedness of an arbitrary word in $\mathcal{A}_g$ in terms of a ``fractional power'' of the symbol $g$, that only depends on the number of appearances of each of the letters $T_g,S_g,M_g$ in the given word.

math.CV↗
arXiv2019

Hankel Bilinear forms on generalized Fock-Sobolev spaces on ${\mathbb C}^n$

We characterize the boundedness of Hankel bilinear forms on a product of generalized Fock-Sobolev spaces on ${\mathbb C}^n$ with respect to the weight $(1+|z|)^ρe^{-\fracα2|z|^{2\ell}}$, for $\ell\ge 1$, $α>0$ and $ρ\in{\mathbb R}$. We obtain a weak decomposition of the Bergman kernel with estimates and a Littlewood-Paley formula, which are key ingredients in the proof of our main results. As an application, we characterize the boundedness, compactness and the membership in the Schatten class of small Hankel operators on these spaces.

math.CV↗
arXiv2017

Small Hankel operators on generalized Fock spaces

We consider Fock spaces $F^{p,\ell}_α$ of entire functions on ${\mathbb C}$ associated to the weights $e^{-α|z|^{2\ell}}$, where $α>0$ and $\ell$ is a positive integer. We compute explicitly the corresponding Bergman kernel associated to $F^{2,\ell}_α$ and, using an adequate factorization of this kernel, we characterize the boundedness and the compactness of the small Hankel operator $\mathfrak{h}^{\ell}_{b,α}$ on $F^{p,\ell}_α$. Moreover, we also determine when $\mathfrak{h}^{\ell}_{b,α}$ is a Hilbert-Schmidt operator on $F^{2,\ell}_α$.

math.CV↗
arXiv2017

Boundedness of the Bergman projection on generalized Fock-Sobolev spaces on ${\mathbb C}^n$

In this paper we solve a problem posed by H. Bommier-Hato, M. Engliš and E.H. Youssfi in [3] on the boundedness of the Bergman-type projections in generalized Fock spaces. It will be a consequence of two facts: a full description of the embeddings between generalized Fock-Sobolev spaces and a complete characterization of the boundedness of the above Bergman type projections between weighted $L^p$-spaces related to generalized Fock-Sobolev spaces.

math.CV↗
arXiv2016

Littlewood-Paley formulas and Carleson measures for weighted Fock spaces induced by $A_\infty$-type weights

We obtain Littlewood-Paley formulas for Fock spaces $\mathcal{F}^q_{β,ω}$ induced by weights $ω\in A^{restricted}_\infty=\cup_{1\le p<\infty}A^{restricted}_{p}$, where $A^{restricted}_{p}$ is the class of weights such that the Bergman projection $P_α$, on the classical Fock space $\mathcal{F}^2_α$, is bounded on $$\mathcal{L}^p_{α,ω}:=\left\{f:\, \int_{\mathbb{C}}|f(z)|^pe^{-p\fracα{2}|z|^2}\,ω(z)dA(z)<\infty \right\}. $$ Using these equivalent norms for $\mathcal{F}^q_{β,ω}$ we characterize the Carleson measures for weighted Fock-Sobolev spaces $\mathcal{F}^{q,n}_{β,ω}$.

math.FA↗
arXiv2013

On multipliers for Hardy-Sobolev spaces and holomorphic potentials

We study the action of some generalized integral operators of Bergman type on pointwise multipliers of holomorphic Triebel-Lizorkin spaces. We construct nontrivial examples of pointwise multipliers in Hardy-Sobolev spaces and give applications of all these results.

math.CV↗
arXiv2013

Bilinear forms on weighted Besov spaces

We compute the norm of some bilinear forms on products of weighted Besov spaces in terms of the norm of their symbol in a space of pointwise multipliers defined in terms of Carleson measures.

math.CV↗
arXiv2010

On integral equations related to weighted Toepitz operators

For weighted Toeplitz operators $\T^N_ϕ$ defined on spaces of holomorphic functions in the unit ball, we derive regularity properties of the solutions $f$ to the integral equation $\T^N_ϕ(f)=h$ in terms of the regularity of the symbol $ϕ$ and the data $h$. As an application, we deduce that if $f\not\equiv0$ is a function in the Hardy space $H^1$ such that its argument $\bar f/f$ is in a Lipschitz space on the unit sphere $\bB$, then $f$ is also in the same Lipschitz space, extending a result of K. Dyakonov to several complex variables.

math.CV↗
arXiv2006

On $L^p$--$L^q$ trace inequalities

We give necessary and sufficient conditions in order that inequalities of the type $$ \| T_K f\|_{L^q(dμ)}\leq C \|f\|_{L^p(dσ)}, \qquad f \in L^p(dσ), $$ hold for a class of integral operators $T_K f(x) = \int_{R^n} K(x, y) f(y) d σ(y)$ with nonnegative kernels, and measures $d μ$ and $dσ$ on $\R^n$, in the case where $p>q>0$ and $p>1$. An important model is provided by the dyadic integral operator with kernel $K_{\mathcal D}(x, y) \sum_{Q\in{\mathcal D}} K(Q) χ_Q(x) χ_Q(y)$, where $\mathcal D=\{Q\}$ is the family of all dyadic cubes in $\R^n$, and $K(Q)$ are arbitrary nonnegative constants associated with $Q \in{\mathcal D}$. The corresponding continuous versions are deduced from their dyadic counterparts. In particular, we show that, for the convolution operator $T_k f = k\star f$ with positive radially decreasing kernel $k(|x-y|)$, the trace inequality $$ \| T_k f\|_{L^q(dμ)}\leq C \|f\|_{L^p(d x)}, \qquad f \in L^p(dx), $$ holds if and only if ${\mathcal W}_{k}[μ] \in L^s (dμ)$, where $s = {\frac{q(p-1)}{p-q}}$. Here ${\mathcal W}_{k}[μ]$ is a nonlinear Wolff potential defined by ${\mathcal W}_{k}[μ](x)=\int_0^{+\infty} k(r) \bar{k}(r)^{\frac 1 {p-1}} μ(B(x,r))^{\frac 1{p-1}} r^{n-1} dr,$ and $\bar{k}(r)=\frac1{r^n}\int_0^r k(t) t^{n-1} dt$. Analogous inequalities for $1\le q < p$ were characterized earlier by the authors using a different method which is not applicable when $q<1$.

math.FA↗