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Geodesics in the Heisenberg Group

Piotr Hajłasz, Scott Zimmerman (2015)

Analysis and Geometry in Metric Spaces

We provide a new and elementary proof for the structure of geodesics in the Heisenberg group Hn. The proof is based on a new isoperimetric inequality for closed curves in R2n.We also prove that the Carnot- Carathéodory metric is real analytic away from the center of the group.

Geometric Fourier analysis

Antonio Cordoba (1982)

Annales de l'institut Fourier

In this paper we continue the study of the Fourier transform on R n , n 2 , analyzing the “almost-orthogonality” of the different directions of the space with respect to the Fourier transform. We prove two theorems: the first is related to an angular Littlewood-Paley square function, and we obtain estimates in terms of powers of log ( N ) , where N is the number of equal angles considered in R 2 . The second is an extension of the Hardy-Littlewood maximal function when one consider cylinders of R n , n 2 , of fixed eccentricity...

Global orthogonality implies local almost-orthogonality.

J. Michael Wilson (2000)

Revista Matemática Iberoamericana

We introduce a new stopping-time argument, adapted to handle linear sums of noncompactly-supported functions that satisfy fairly weak decay, smoothness, and cancellation conditions. We use the argument to obtain a new Littlewood-Paley-type result for such sums.

Good-λ inequalities for wavelets of compact support

Sarah V. Cook (2004)

Colloquium Mathematicae

For a wavelet ψ of compact support, we define a square function S w and a maximal function NΛ. We then obtain the L p equivalence of these functions for 0 < p < ∞. We show this equivalence by using good-λ inequalities.

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