Óscar Ciaurri

Transplantation and multiplier theorems for Fourier-Bessel expansions

Proved are weighted transplantation inequalities for Fourier-Bessel expansions. These extend known results on this subject by considering the largest possible range of parameters, allowing more weights and admitting a shift. The results are then used to produce a fairly general multiplier theorem with power weights for considered expansions. Also fractional integral results and conjugate function norm inequalities for these expansions are proved.

Weighted transplantation for Fourier-Bessel series

We prove weighted transplantation inequalities for Fourier-Bessel series with weights more general than previously considered power weights. These inequalities follow by using a local version of the Calderón-Zygmund operator theory. The approach also allows us to obtain weighted weak type (1, 1) inequalities. As a typical application of transplantation inequalities, a multiplier result for the expansions considered is proved within a weighted setting with general weights.

Harmonic analysis associated with a discrete Laplacian

It is well known that the fundamental solution of

The Riesz Transform for the Harmonic Oscillator in Spherical Coordinates

{u_t}\left( {n,t} \right) = u\left( {n + 1,t} \right) - 2u\left( {n,t} \right) + u\left( {n - 1,t} \right),n \in \mathbb{Z},

An uiniform boundedness for Bochner–Riesz operators related to the Hankel transform

ut(n,t)=u(n+1,t)−2u(n,t)+u(n−1,t),n∈ℤ, with u(n, 0) = δnm for every fixed m ∈ Z is given by u(n, t) = e−2tIn−m(2t), where Ik(t) is the Bessel function of imaginary argument. In other words, the heat semigroup of the discrete Laplacian is described by the formal series Wtf(n) = Σm∈Ze−2tIn−m(2t)f(m). This formula allows us to analyze some operators associated with the discrete Laplacian using semigroup theory. In particular, we obtain the maximum principle for the discrete fractional Laplacian, weighted ℓp(Z)-boundedness of conjugate harmonic functions, Riesz transforms and square functions of Littlewood-Paley. We also show that the Riesz transforms essentially coincide with the so-called discrete Hilbert transform defined by D. Hilbert at the beginning of the twentieth century. We also see that these Riesz transforms are limits of the conjugate harmonic functions. The results rely on a careful use of several properties of Bessel functions.

On a connection between the discrete fractional Laplacian and superdiffusion

Abstract We present a new simple proof of Euler’s formulas for ζ(2k), where k = 1, 2, 3,…. The computation is done using only the defining properties of the Bernoulli polynomials and summing a telescoping series. The same method also yields integral formulas for ζ(2k + 1).

Euler's Product Expansion for the Sine: An Elementary Proof

In this paper, we show weighted estimates in mixed norm spaces for the Riesz transform associated with the harmonic oscillator in spherical coordinates. In order to prove the result, we need a weighted inequality for a vector-valued extension of the Riesz transform related to the Laguerre expansions that is of independent interest. The main tools to obtain such an extension are a weighted inequality for the Riesz transform independent of the order of the involved Laguerre functions and an appropriate adaptation of Rubio de Francia’s extrapolation theorem.

Discrete Fourier-Neumann series

Abstract In the context of the Dunkl transform a complete orthogonal system arises in a very natural way. This paper studies the weighted norm convergence of the Fourier series expansion associated to this system. We establish conditions on the weights, in terms of the A p classes of Muckenhoupt, which ensure the convergence. Necessary conditions are also proved, which for a wide class of weights coincide with the sufficient conditions.