arXiv subjects

S. Pérez-Esteva

Publications and source records attributed to S. Pérez-Esteva.

4 recordsLinked to original sources

arXiv2024

Spectral cluster asymptotics of the Dirichlet to Neumann operator on the two-sphere

We study the spectrum of the Dirichlet to Neumann operator of the two-sphere associated to a Schrödinger operator in the unit ball. The spectrum forms clusters of size $O(1/k)$ around the sequence of natural numbers $k=1,2,\ldots$, and we compute the first three terms in the asymptotic distribution of the eigenvalues within the clusters, as $k\to\infty$ (band invariants). There are two independent aspects of the proof. The first is a study of the Berezin symbol of the Dirichlet to Neumann operator, which arises after one applies the averaging method. The second is the use of a symbolic calculus of Berezin-Toeplitz operators on the manifold of closed geodesics of the sphere.

math.SP↗

arXiv2020

The Fourier extension operator of distributions in Sobolev spaces of the sphere and the Helmholtz equation

The purpose of this paper is to characterize all the entire solutions of the homogeneous Helmholtz equation (solutions in $\mathbb{R}^d$) arising from the Fourier extension operator of distributions in Sobolev spaces of the sphere $H^α(\mathbb{S}^{d-1}),$ with $α\in \mathbb{R}$. We present two characterizations. The first one is written in terms of certain $L^2$-weighted norms involving real powers of the spherical Laplacian. The second one is in the spirit of the classical description of the Herglotz wave functions given by P. Hartman and C. Wilcox. For $α>0$ this characterization involves a multivariable square function evaluated in a vector of entire solutions of the Helmholtz equation, while for $α<0$ it is written in terms of an spherical integral operator acting as a fractional integration operator. Finally, we also characterize all the solutions that are the Fourier extension operator of distributions in the sphere.

math.CA↗

arXiv2019

Perturbations of the Landau Hamiltonian: Asymptotics of eigenvalue clusters

We consider the asymptotic behavior of the spectrum of the Landau Hamiltonian plus a rapidly decaying potential, as the magnetic field strength, $B$, tends to infinity. After a suitable rescaling, this becomes a semiclassical problem where the role of Planck's constant is played by $1/B$. The spectrum of the operator forms eigenvalue clusters. We obtain a Szegő limit theorem for the eigenvalues in the clusters as a suitable cluster index and $B$ tend to infinity with a fixed ratio $\calE$. The answer involves the averages of the potential over circles of radius $\sqrt{\calE/2}$ (circular Radon transform). We also discuss related inverse spectral results.

math-ph↗

arXiv2019

Characterization of Sobolev spaces on the sphere

We prove a characterization of the Sobolev spaces $H^α$ on the unit sphere $\mathbb{S}^{d-1}$, where the smoothness index $α$ is any positive real number and $d\geq 2$. This characterization does not use differentiation and it is given in terms of $([α/2]+1)$-multidimensional square functions $S_α$. For $[α/2]=0,$ a function $f\in L^2(\mathbb{S}^{d-1})$ belongs to $H^α(\mathbb{S}^{d-1})$ if and only if $S_α(f)\in L^2(\mathbb{S}^{d-1})$. If $n=[α/2]>0$, the membership of $f$ is equivalent to the existence of $g_1,\cdots,g_n$ in $L^2(\mathbb{S}^{d-1})$ such that $S_α(f,g_1,\ldots,g_n)\in L^2(\mathbb{S}^{d-1})$ and in this case, $g_j=T_j((-Δ_S)^j f)$, where $T_j$ is a zonal Fourier multiplier in the sphere and $Δ_S$ is the Laplace-Beltrami operator. The square functions $S_α$ are based on averaging operators over euclidean balls (caps) in the sphere that may be viewed as zonal multipliers. The results in the paper are in the spirit of the characterization of fractional Sobolev spaces given in $\mathbb{R}^d$ proved in \cite{AMV}. The development of the theory is fully based on zonal Fourier multipliers and special functions.

math.CA↗