We observe that the classical theorem of Hardy on Fourier transform pairs can be reformulated in terms of the heat kernel associated with the Laplacian on the Euclidean space. This leads to an interesting version of Hardy's theorem for the sublaplacian on the Heisenberg group. We also consider certain Rockland operators on the Heisenberg group and Schrödinger operators on ℝⁿ related to them.
2
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
We study $L^p$ norm convergence of Bochner-Riesz means $S_R^δ f$ associated with certain non-negative differential operators. When the kernel $S_R^m(x,y)$ satisfies a weak estimate for large values of m we prove $L^p$ norm convergence of $S_R^δ f$ for δ > n|1/p-1/2|, 1 < p < ∞, where n is the dimension of the underlying manifold.
4
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
We prove an analogue of Gutzmer's formula for Hermite expansions. As a consequence we obtain a new proof of a characterisation of the image of L²(ℝⁿ) under the Hermite semigroup. We also obtain some new orthogonality relations for complexified Hermite functions.
5
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
Let G be a semisimple Lie group with Iwasawa decomposition G = KAN. Let X = G/K be the associated symmetric space and assume that X is of rank one. Let M be the centraliser of A in K and consider an orthonormal basis ${Y_{δ,j}: δ ∈ K̂₀, 1 ≤ j ≤ d_{δ}}$ of L²(K/M) consisting of K-finite functions of type δ on K/M. For a function f on X let f̃(λ,b), λ ∈ ℂ, be the Helgason Fourier transform. Let $h_{t}$ be the heat kernel associated to the Laplace-Beltrami operator and let $Q_{δ}(iλ + ϱ)$ be the Kostant polynomials. We establish the following version of Hardy's theorem for the Helgason Fourier transform: Let f be a function on G/K which satisfies $|f(ka_{r})| ≤ Ch_{t}(r)$. Further assume that for every δ and j the functions $F_{δ,j}(λ) = Q_{δ}(iλ +ϱ)^{-1} ∫_{K/M} f̃(λ,b)Y_{δ,j}(b)db$ satisfy the estimates $|F_{δ,j}(λ)| ≤ C_{δ,j}e^{-tλ²}$ for λ ∈ ℝ. Then f is a constant multiple of the heat kernel $h_{t}$.
6
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
Let ℒ be the sublaplacian on the Heisenberg group Hⁿ. A recent result of Müller and Stein shows that the operator $ℒ^{-1/2} sin√ℒ$ is bounded on $L^{p}(Hⁿ)$ for all p satisfying |1/p - 1/2| < 1/(2n). In this paper we show that the same operator is bounded on $L^{p}$ in the bigger range |1/p - 1/2| < 1/(2n-1) if we consider only functions which are band limited in the central variable.
7
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
We prove a restriction theorem for the class-1 representations of the Heisenberg motion group. This is done using an improvement of the restriction theorem for the special Hermite projection operators proved in [13]. We also prove a restriction theorem for the Heisenberg group.