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Estimates of fundamental solution for Kohn Laplacian in Besov and Triebel-Lizorkin spaces
Published in Applicable Analysis, 2023
Tongtong Qin, Der-Chen Chang, Yongsheng Han, Xinfeng Wu
Inspired by the works of Beals-Greiner [15], Beals-Gaveau-Greiner [16–19] and Greiner-Li [20] we shall use the complex and real Hamiltonian and Lagrangian formalism developed in the sub-Riemannian manifolds to look for the fundamental solution of , i.e. a distribution in which satisfies
Since the operator is translation invariant along the t-direction, hence, we may assume that . We shall look for a in the form
Here, the functions g, E and have significant geometric meanings and we will give a brief discussion here. More precisely, let
be the Hamilton function with the variables dual to . The bicharacteristic curves are complex, a consequence of nonstandard boundary conditions. It is known that the function g is given by an action integral in terms of these bicharacteristics. The format (5) has a simple geometric interpretation. The operator of (1) has a characteristic variety in the cotangent bundle given by .