Sundaram Thangavelu – författare

The interplay between analysis on Lie groups and the theory of special functions is well known. This monograph deals with the case of the Heisenberg group and the related expansions in terms of Hermite, special Hermite, and Laguerre functions. The main thrust of the book is to develop a concrete Littlewood-Paley-Stein theory for these expansions and use the theory to prove multiplier theorems. The questions of almost-everywhere and mean convergence of Bochner-Riesz means are also treated. Most of the results in this monograph appear for the first time in book form.

The Heisenberg group has been implicitly present in much of mathematics and physics for a long time. Thangavelu's work is developed within the framework of harmonic analysis (Fourier transforms, convolution algebra, and related ideas) and gives a survey of the field. Additionally the author discusses in detail the representation theory of the group and its relationship to the theory of classical special functions. Among the topics covered are the Plancherel and Paley-Wiener theorems, spectral theory of the sublaplacian, Wiener-Tauberian theorems, Bocher-Riesz means and multipliers for the Fourier transform. The exposition is systematic, and leads to several problems and conjectures for further consideration. Any reader who is interested in pursuing research on the Heisenberg group should find this text of use.

The central theme of this work is the development of a number of analogs of Hardy's theorem, which is one interpretation of the mathematical Uncertainty Principle, in settings arising from noncommutative harmonic analysis. A tutorial introduction gives the requisite background material. The techniques used to prove the main results run the gamut of modern harmonic analysis such as representation theory, spherical functions, Hecke-Bochner formulas and special functions. Graduate students and researchers in harmonic analysis will greatly benefit from this unique book.

In 1932 Norbert Wiener gave a series of lectures on Fourier analysis at the Univer­ sity of Cambridge. One result of Wiener's visit to Cambridge was his well-known text The Fourier Integral and Certain of its Applications; another was a paper by G. H. Hardy in the 1933 Journalofthe London Mathematical Society. As Hardy says in the introduction to this paper, This note originates from a remark of Prof. N. Wiener, to the effect that "a f and g [= j] cannot both be very small". ... The theo­ pair of transforms rems which follow give the most precise interpretation possible ofWiener's remark. Hardy's own statement of his results, lightly paraphrased, is as follows, in which f is an integrable function on the real line and f is its Fourier transform: x 2 m If f and j are both 0 (Ix1e- /2) for large x and some m, then each is a finite linear combination ofHermite functions. In particular, if f and j are x2 x 2 2 2 both O(e- / ), then f = j = Ae- / , where A is a constant; and if one x 2 2 is0(e- / ), then both are null.