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Some remarks on Bochner-Riesz means

S. Thangavelu — 2000

Colloquium Mathematicae

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.

An analogue of Hardy's theorem for the Heisenberg group

S. Thangavelu — 2001

Colloquium Mathematicae

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.

Hardy's theorem for the helgason Fourier transform on noncompact rank one symmetric spaces

S. Thangavelu — 2002

Colloquium Mathematicae

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 K ̂ , 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 ( i λ + ϱ ) be the Kostant polynomials. We establish the following version...

An analogue of Gutzmer's formula for Hermite expansions

S. Thangavelu — 2008

Studia Mathematica

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.

Oscillating multipliers on the Heisenberg group

E. K. NarayananS. Thangavelu — 2001

Colloquium Mathematicae

Let ℒ be the sublaplacian on the Heisenberg group Hⁿ. A recent result of Müller and Stein shows that the operator - 1 / 2 s i n is bounded on L p ( H ) 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.

A spectral Paley-Wiener theorem for the Heisenberg group and a support theorem for the twisted spherical means on n

E. K. NarayananS. Thangavelu — 2006

Annales de l’institut Fourier

We prove a spectral Paley-Wiener theorem for the Heisenberg group by means of a support theorem for the twisted spherical means on n . If f ( z ) e 1 4 | z | 2 is a Schwartz class function we show that f is supported in a ball of radius B in n if and only if f × μ r ( z ) = 0 for r &gt; B + | z | for all z n . This is an analogue of Helgason’s support theorem on Euclidean and hyperbolic spaces. When n = 1 we show that the two conditions f × μ r ( z ) = μ r × f ( z ) = 0 for r &gt; B + | z | imply a support theorem for a large class of functions with exponential growth. Surprisingly enough,this latter...

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