Inserted: 22 jun 2022
Last Updated: 3 jun 2023
Journal: Journal of Spectral Theory
In this article, we investigate spectral properties of the sublaplacian $−\Delta_G$ on the Engel group, which is the main example of a Carnot group of step 3. We develop a new approach to the Fourier analysis on the Engel group in terms of a frequency set. This enables us to give fine estimates on the convolution kernel satisfying $F(−\Delta_G)u=u*k_F$, for suitable scalar functions $F$, and in turn to obtain proofs of classical functional embeddings, via Fourier techniques. This analysis requires a summability property on the spectrum of the quartic oscillator, which we obtain by means of semiclassical techniques and which is of independent interest.