Spectrum of the Kohn Laplacian on the Rossi sphere

We study the spectrum of the Kohn Laplacian $\square_b^t$ on the Rossi example $(\mathbb{S}^3, \mathcal{L}_t)$. In particular we show that $0$ is in the essential spectrum of $\square_b^t$, which yields another proof of the global non-embeddability of the Rossi example.