Pseudohermitian invariants and classification of CR mappings in generalized ellipsoids

We discuss the problem of classifying all local CR diffeomorphisms of a strictly pseudoconvex surface. Our method exploits the Tanaka--Webster pseudohermitian invariants, their transformation formulae, and the Chern--Moser invariants. Our main application concerns a class of generalized ellipsoids where we classify all local CR mappings.Comment: Accepted version, to appear on J. Math. Soc. Japa

Improved Lipschitz approximation of HH-perimeter minimizing boundaries

We prove two new approximation results of $H$-perimeter minimizing boundaries by means of intrinsic Lipschitz functions in the setting of the Heisenberg group $\mathbb{H}^n$ with $n\ge2$. The first one is an improvement of a result of Monti and is the natural reformulation in $\mathbb{H}^n$ of the classical Lipschitz approximation in $\mathbb{R}^n$. The second one is an adaptation of the approximation via maximal function developed by De Lellis and Spadaro.Comment: 25 page

On tangent cones to length minimizers in Carnot-Carath\'eodory spaces

We give a detailed proof of some facts about the blow-up of horizontal curves in Carnot-Carath\'eodory spaces.Comment: 19 page

Quantitative isoperimetric inequalities in H^n

In the Heisenberg group H^n, we prove quantitative isoperimetric inequalities for Pansu's spheres, that are known to be isoperimetric under various assumptions. The inequalities are shown for suitably restricted classes of competing sets and the proof relies on the construction of sub-calibrations

The regularity problem for geodesics of the control distance

In this survey, we present some recent results on the problem about the regularity of length-minimizing curves in sub-Riemannian geometry. We also sketch the possible application of some ideas coming from Geometric Measure Theory

Extremal polynomials in stratified groups

We introduce a family of extremal polynomials associated with the prolongation of a stratified nilpotent Lie algebra. These polynomials tre related to a new algebraic characterization of abnormal sub-Riemannian extremals in stratified nilpotent Lie groups. They satisfy a set of remarkable structure relations that are used to integrate the adjoint equations, in both normal and abnormal case

Isoperimetric inequality in the Grushin plane

We prove a sharp isoperimetric inequality in the Grushin plane and compute the corresponding isoperimetric set

Height estimate and slicing formulas in the Heisenberg group

We prove a height-estimate (distance from the tangent hyperplane) for Lambda-minima of the perimeter in the sub-Riemannian Heisenberg group. The estimate is in terms of a power of the excess (L^2-mean oscillation of the normal) and its proof is based on a new coarea formula for rectifiable sets in the Heisenberg group