Title: First eigenvalue estimates in pseudo-hermitian geometry
Abstract: In this talk, I will talk about how to get a sharp lower bound estimate for the first nonzero eigenvalue of the sub-Laplacian, Kohn Laplacian, Folland-Stein operator, weighted sub-Laplacian and weighted Kohn Laplacian on a closed strictly pseudo-convex CR (2n+1)-manifold. We also discuss the case when a sharp lower bound estimate of the sub-Laplacian, Kohn Laplacian, weighted sub-Laplacian or weighted Kohn Laplacian is achieved. It can be showed that such a manifold is isometric to the standard CR (2n+1)-sphere.