Download An Introduction to the Heisenberg Group and the by Luca Capogna, Donatella Danielli, Scott D. Pauls, Jeremy PDF

By Luca Capogna, Donatella Danielli, Scott D. Pauls, Jeremy Tyson

The earlier decade has witnessed a dramatic and common enlargement of curiosity and job in sub-Riemannian (Carnot-Caratheodory) geometry, stimulated either internally via its function as a easy version within the smooth idea of research on metric areas, and externally during the non-stop improvement of functions (both classical and rising) in components equivalent to regulate concept, robot direction making plans, neurobiology and electronic photograph reconstruction. The imperative instance of a sub Riemannian constitution is the Heisenberg staff, that's a nexus for all the aforementioned purposes in addition to some extent of touch among CR geometry, Gromov hyperbolic geometry of advanced hyperbolic area, subelliptic PDE, jet areas, and quantum mechanics. This e-book presents an advent to the fundamentals of sub-Riemannian differential geometry and geometric research within the Heisenberg crew, focusing totally on the present kingdom of data concerning Pierre Pansu's celebrated 1982 conjecture in regards to the sub-Riemannian isoperimetric profile. It provides an in depth description of Heisenberg submanifold geometry and geometric degree conception, which gives a chance to assemble for the 1st time in a single place a few of the recognized partial effects and techniques of assault on Pansu's challenge. As such it serves at the same time as an creation to the realm for graduate scholars and starting researchers, and as a learn monograph thinking about the isoperimetric challenge appropriate for specialists within the area.

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Extra resources for An Introduction to the Heisenberg Group and the Sub-Riemannian Isoperimetric Problem

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Y˜n } is orthonormal. Note that limL→∞ Y˜i = 0 and again, the only curves with finite velocity in the limit are the horizontal ones. 34 Chapter 2. The Heisenberg Group and Sub-Riemannian Geometry The convergence of geodesic arcs in this more general (higher step) setting is quite delicate and presents an obstacle which does not appear in the step two case: the Riemannian geodesics in the approximants may converge to singular geodesics. This line of investigation goes beyond the scope of this survey and we refer the reader to the monograph [203] for more details.

25) 4 To simplify the notation we dilate this ball by a factor of 2 and translate vertically by −πR2 /2. 26) R2 − r 2 , are the conjectured extremals for the sub-Riemannian isoperimetric problem in H and are often called bubble sets. 3 and the introduction to Chapter 8. 3. We emphasize that the boundary of the set B(o, R) is C 2 but not C 3 . 4 Riemannian approximants to H The Heisenberg group equipped with the CC metric may be realized as the Gromov–Hausdorff limit of a sequence of Riemannian manifolds (R3 , gL ), as L → ∞.

I=1 Observe that the homogeneous dimension of Hn is 2n + 2. 3. The Haar measure on G coincides with the push-forward of the Lebesgue measure on the Lie algebra g under the exponential map. It is easy to verify that the Jacobian determinant of the dilation δs : G → G is constant, equal to sQ . As with the Heisenberg group, we define the horizontal gradient of a C 1 function f : G → R by m1 ∇0 f = X1j f X1j . j=1 At various points in this survey we will work in this general setting to emphasize the fact that certain results do not depend on the special structure of H.

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